the history of earth presentation

Historical Geology

A free online textbook for Historical Geology courses

A Brief History of Earth

After reading this chapter, students should be able to:

• Describe the origins the of the Universe in the context of Big Bang theory
• Describe the origins of our solar system in the context of nebular theory
• Identify major tectonic and biologic events that occurred in various geologic eons

Based on An Introduction to Geology, Chapter 8: Earth History

Entire courses and careers have been based on the wide-ranging topics covering Earth’s history. Throughout the long history of Earth, change has been the norm. Looking back in time, an untrained eye would see many unfamiliar life forms and terrains. The main topics studied in Earth history are paleogeography, paleontology, and paleoecology and paleoclimatology —respectively, past landscapes, past organisms, past ecosystems, and past environments. This chapter will cover (briefly) the origin of the universe and the 4.6 billion year history of Earth. It will act as a guide, linking out to other chapters, case studies, and sections in this book.

Origin of the Universe

The universe appears to have an infinite number of galaxies and solar systems and our solar system occupies a small section of this vast entirety. The origins of the universe and solar system set the context for conceptualizing the Earth’s origin and early history.

Big-Bang Theory

The big-bang theory proposes the universe was formed from an infinitely dense and hot core of material. The bang in the title suggests there was an explosive, outward expansion of all matter and space that created atoms. Spectroscopy confirms that hydrogen makes up about 74% of all matter in the universe. Since its creation, the universe has been expanding for 13.8 billion years and recent observations suggest the rate of this expansion is increasing . 

Spectroscopy

Cosmic Microwave Background Radiation

Stellar Evolution

Birth of a star.

Death of a Star

The death of a star can range from spectacular to other-worldly (see figure). Stars like the Sun form a planetary nebula, which comes from the collapse of the star’s outer layers in an event like the implosion of a building. In the tug-of-war between gravity’s inward pull and fusion’s outward push, gravity instantly takes over when fusion ends, with the outer gasses puffing away to form a nebula. More massive stars do this as well but with a more energetic collapse, which starts another type of energy release mixed with element creation known as a supernova. In a supernova , the collapse of the core suddenly halts, creating a massive outward-propagating shock wave. A supernova is the most energetic explosion in the universe short of the big bang. The energy release is so significant the ensuing fusion can make every element up through uranium .

The death of the star can result in the creation of white dwarfs, neutron stars, or black holes. Following their deaths, stars like the Sun turn into white dwarfs .

White dwarfs are hot star embers, formed by packing most of a dying star’s mass into a small and dense object about the size of Earth. Larger stars may explode in a supernova that packs their mass even tighter to become neutron stars. Neutron stars are so dense that protons combine with electrons to form neutrons. The largest stars collapse their mass even further, becoming objects so dense that light cannot escape their gravitational grasp. These are the infamous black holes and the details of the physics of what occurs in them are still up for debate.

Origin of the Solar System: The Nebular Hypothesis

Planet Arrangement and Segregation

Pluto and planet definition

Geoscientists use the geological time scale to assign relative age names to events and rocks, separating major events in Earth’s history based on significant changes as recorded in rocks and fossils. This section summarizes the most notable events of each major time interval. For a breakdown on how these time intervals are chosen and organized, see chapter 7 .

The Hadean Eon, named after the Greek god and ruler of the underworld Hades, is the oldest eon and dates from 4.5–4.0 billion years ago .  

Origin of Earth’s Crust

Origin of the Moon

Computer simulation of the evolution of the Moon (2 minutes).

Origin of Earth’s Water

Archean Eon

Late Heavy Bombardment

Objects were chaotically flying around at the start of the solar system, building the planets and moons. There is evidence that after the planets formed, about 4.1–3.8 billion years ago, a second large spike of asteroid and comet impacted the Earth and Moon in an event called late heavy bombardment . Meteorites and comets in stable or semi-stable orbits became unstable and started impacting objects throughout the solar system. In addition, this event is called the lunar cataclysm because most of the Moons craters are from this event. During late heavy bombardment, the Earth, Moon, and all planets in the solar system were pummeled by material from the asteroid and Kuiper belts. Evidence of this bombardment was found within samples collected from the Moon.

Origin of the Continents

The first solid evidence of modern plate tectonics is found at the end of the Archean, indicating at least some continental lithosphere must have been in place. This evidence does not necessarily mark the starting point of plate tectonics; remnants of earlier tectonic activity could have been erased by the rock cycle .

The stable interiors of the current continents are called cratons and were mostly formed in the Archean Eon. A craton has two main parts: the shield , which is crystalline basement rock near the surface, and the platform made of sedimentary rocks covering the shield. Most cratons have remained relatively unchanged with most tectonic activity having occurred around cratons instead of within them. Whether they were created by plate tectonics or another process, Archean continents gave rise to the Proterozoic continents that now dominate our planet.

First Life on Earth

Although the origin of life on Earth is unknown, hypotheses include a chemical origin in the early atmosphere and ocean, deep-sea hydrothermal vents, and delivery to Earth by comets or other objects. One hypothesis is that life arose from the chemical environment of the Earth’s early atmosphere and oceans, which was very different than today. The oxygen-free atmosphere produced a reducing environment with abundant methane, carbon dioxide, sulfur, and nitrogen compounds. This is what the atmosphere is like on other bodies in the solar system. In the famous Miller-Urey experiment, researchers simulated early Earth’s atmosphere and lightning within a sealed vessel. After igniting sparks within the vessel, they discovered the formation of amino acids, the fundamental building blocks of proteins.  In 1977, when scientists discovered an isolated ecosystem around hydrothermal vents on a deep-sea mid-ocean ridge (see Chapter 4 ), it opened the door for another explanation of the origin of life. The hydrothermal vents have a unique ecosystem of critters with chemosynthesis as the foundation of the food chain instead of photosynthesis. The ecosystem is deriving its energy from hot chemical-rich waters pouring out of underground towers. This suggests that life could have started on the deep ocean floor and derived energy from the heat from the Earth’s interior via chemosynthesis. Scientists have since expanded the search for life to more unconventional places, like Jupiter’s icy moon Europa.

Animation of the original Miller-Urey 1959 experiment that simulated the early atmosphere and created amino acids from simple elements and compounds.

Another possibility is that life or its building blocks came to Earth from space, carried aboard comets or other objects. Amino acids, for example, have been found within comets and meteorites. This intriguing possibility also implies a high likelihood of life existing elsewhere in the cosmos.

Proterozoic Eon

An oxygenated world also changed the chemistry of the planet in significant ways. For example, iron remained in solution in the non-oxygenated environment of the earlier Archean Eon. In chemistry, this is known as a reducing environment. Once the environment was oxygenated, iron combined with free oxygen to form solid precipitates of iron oxide, such as the mineral hematite or magnetite. These precipitates accumulated into large mineral deposits with red chert known as banded-iron formations, which are dated at about 2 billion years .

The disagreements over these complex reconstructions is exemplified by geologists proposing at least six different models for the breakup of Rodinia to create Australia , Antarctica , parts of China , the Tarim craton north of the Himalaya , Siberia , or the Kalahari craton of eastern Africa . This breakup created lots of shallow-water, biologically favorable environments that fostered the evolutionary breakthroughs marking the start of the next eon, the Phanerozoic.

Life Evolves

Another important event in Earth’s biological history occurred about 1.2 billion years ago when eukaryotes invented sexual reproduction. Sharing genetic material from two reproducing individuals, male and female, greatly increased genetic variability in their offspring. This genetic mixing accelerated evolutionary change, contributing to more complexity among individual organisms and within ecosystems (see Chapter 7 ).

Proterozoic land surfaces were barren of plants and animals and geologic processes actively shaped the environment differently because land surfaces were not protected by leafy and woody vegetation. For example, rain and rivers would have caused erosion at much higher rates on land surfaces devoid of plants. This resulted in thick accumulations of pure quartz sandstone from the Proterozoic Eon such as the extensive quartzite formations in the core of the Uinta Mountains in Utah.

Phanerozoic Eon: Paleozoic Era

Life in the early Paleozoic Era was dominated by marine organisms but by the middle of the era plants and animals evolved to live and reproduce on land . Fish evolved jaws and fins evolved into jointed limbs. The development of lungs allowed animals to emerge from the sea and become the first air-breathing tetrapods (four-legged animals) such as amphibians. From amphibians evolved reptiles with the amniotic egg. From reptiles evolved an early ancestor to birds and mammals  and their scales became feathers and fur. Near the end of the Paleozoic Era, the Carboniferous Period had some of the most extensive forests in Earth’s history. Their fossilized remains became the coal that powered the industrial revolution

Paleozoic Tectonics and Paleogeography

During the Paleozoic Era, sea-levels rose and fell four times. With each sea-level rise, the majority of North America was covered by a shallow tropical ocean. Evidence of these submersions are the abundant marine sedimentary rocks such as limestone with fossils corals and ooids. Extensive sea-level falls are documented by widespread unconformities. Today, the midcontinent has extensive marine sedimentary rocks from the Paleozoic and western North America has thick layers of marine limestone on block faulted mountain ranges such as Mt. Timpanogos near Provo, Utah . 

Animation of plate movement the last 3.3 billion years. Pangea occurs at the 4:40 mark.

While the east coast of North America was tectonically active during the Paleozoic Era, the west coast remained mostly inactive as a passive margin during the early Paleozoic. The western edge of North American continent was near the present-day Nevada-Utah border and was an expansive shallow continental shelf near the paleoequator. However, by the Devonian Period, the Antler orogeny started on the west coast and lasted until the Pennsylvanian Period. The Antler orogeny was a volcanic island arc that was accreted onto western North America with the subduction direction away from North America. This created a mountain range on the west coast of North American called the Antler highlands and was the first part of building the land in the west that would eventually make most of California, Oregon, and Washington states. By the late Paleozoic, the Sonoma orogeny began on the west coast and was another collision of an island arc. The Sonoma orogeny marks the change in subduction direction to be toward North America with a volcanic arc along the entire west coast of North America by late Paleozoic to early Mesozoic Eras .

By the end of the Paleozoic Era, the east coast of North America had a very high mountain range due to continental collision and the creation of Pangea. The west coast of North America had smaller and isolated volcanic highlands associated with island arc accretion. During the Mesozoic Era, the size of the mountains on either side of North America would flip, with the west coast being a more tectonically active plate boundary and the east coast changing into a passive margin after the breakup of Pangea.

Paleozoic Evolution

According to evidence from glacial deposits, a small ice age caused sea-levels to drop and led to a major mass extinction by the end of the Ordovician. This is the earliest of five mass extinction events documented in the fossil record. During this mass extinction, an unusually large number of species abruptly disappear in the fossil record (see video). 

4-minute video describing mass extinctions.

 Land plants had also evolved into the first trees and forests . Toward the end of the Devonian, another mass extinction event occurred. This extinction, while severe, is the least temporally defined, with wide variations in the timing of the event or events. Reef building organisms were the hardest hit, leading to dramatic changes in marine ecosystems .

Permian Mass Extinction

Phanerozoic Eon: Mesozoic Era

8.7.1 Mesozoic Tectonics and Paleogeography

This age pattern shows how the Atlantic Ocean opened as the young Mid-Atlantic Ridge began to create the seafloor. This means the Atlantic ocean started opening and was first formed here. The southern Atlantic opened next, with South America separating from central and southern Africa. Last (happening after the Mesozoic ended) was the northernmost Atlantic, with Greenland and Scandinavia parting ways.  The breaking points of each rifted plate margin eventually turned into the passive plate boundaries of the east coast of the Americas today.

Video of Pangea breaking apart and plates moving to their present locations. By Tanya Atwater.

Tectonics had an influence in one more important geographic feature in North America: the Cretaceous Western Interior Foreland Basin, which flooded during high sea levels forming the Cretaceous Interior Seaway . Subduction from the west was the Farallon Plate, an oceanic plate connected to the Pacific Plate (seen today as remnants such as the Juan de Fuca Plate, off the coast of the Pacific Northwest). Subduction was shallow at this time because a very young, hot and less dense portion of the Farallon plate was subducted. This shallow subduction caused a downwarping in the central part of North America . High sea levels due to shallow subduction, and increasing rates of seafloor spreading and subduction, high temperatures, and melted ice also contributed to the high sea levels . These factors allowed a shallow epicontinental seaway that extended from the Gulf of Mexico to the Arctic Ocean to divide North America into two separate land masses , Laramidia to the west and Appalachia to the east, for 25 million years . Many of the coal deposits in Utah and Wyoming formed from swamps along the shores of this seaway . By the end of the Cretaceous, cooling temperatures caused the seaway to regress .

8.7.2 Mesozoic Evolution

K-T Extinction

Similar to the end of the Paleozoic era, the Mesozoic Era ended with the K-Pg Mass Extinction (previously known as the K-T Extinction ) 66 million years ago . This extinction event was likely caused by a large bolide ( an extraterrestrial impactor such as an asteroid, meteoroid, or comet) that collided with earth . Ninety percent of plankton species, 75% of plant species, and all the dinosaurs went extinct at this time.

Phanerozoic Eon: Cenozoic Era

8.8.1 Cenozoic Tectonics and Paleogeography

Animation of the last 38 million years of movement in western North America. Note, that after the ridge is subducted, convergent turns to transform (with divergent inland).

8.8.2 Cenozoic Evolution

Anthropocene and Extinction

The changes that have occurred since the inception of Earth are vast and significant. From the oxygenation of the atmosphere, the progression of life forms, the assembly and deconstruction of several supercontinents, to the extinction of more life forms than exist today, having a general understanding of these changes can put present change into a more rounded perspective.

Chapter Contents

• 1.1.1.1 Spectroscopy
• 1.1.1.2 Redshift
• 1.1.1.3 Cosmic Microwave Background Radiation
• 1.1.2.1 Birth of a star
• 1.1.2.2 Fusion
• 1.1.2.3 Death of a Star
• 1.2.1.1 Pluto and planet definition
• 1.3.1 Origin of Earth’s Crust
• 1.3.2 Origin of the Moon
• 1.3.3 Origin of Earth’s Water
• 1.4.1 Late Heavy Bombardment
• 1.4.2 Origin of the Continents
• 1.4.3 First Life on Earth
• 1.5.1 Rodinia
• 1.5.2 Life Evolves
• 1.6.1 Paleozoic Tectonics and Paleogeography
• 1.6.2.1 Permian Mass Extinction
• 1.7.1 8.7.1 Mesozoic Tectonics and Paleogeography
• 1.7.2.1 K-T Extinction
• 1.8.1 8.8.1 Cenozoic Tectonics and Paleogeography
• 1.8.2.1 Anthropocene and Extinction
• 1.9 Summary
• 1.10 References

Ch. 12: History of Life on Earth

Earth’s History

• All cells come from preexisting cells. Where did the 1 st cells come from?
• Models approximating early earth’s conditions reconstruct life originating processes.

12-1: How Did Life Begin?

The Age of Earth

• Earth formed 4.5 billion years ago
• Cooling of Earth allowed water vapor in the atmosphere to condense into oceans
• Life most likely evolved in the oceans over a period of hundreds of millions of years
• Earth’s age is estimated by measuring the age of rocks

Measuring Earth’s Age

• Radiometric dating: way to determine the age of something by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
• Isotopes = atoms of the same element with different atomic masses
• C-12 = 6 protons + 6 neutrons; C-14 = 6 protons + 8 neutrons
• Radioisotope : radioactive isotopes that are unstable and undergo radioactive decay, releasing particles and energy (radiation)
• Half-life = length of time it takes for one-half of the mass of the parent isotope to decay into a daughter isotope
• Use rate of decay to estimate age of fossils/rock material

Formation of the Basic Chemicals of Life

• Life on Earth developed through chemical and physical processes
• Life probably arose from the chemical reaction of molecules of nonliving matter
• These chemical reactions were energized by the sun and volcanic heat
• The resulting more complex, organic molecules probably became the building blocks of the first cells
• This hypothesis has been tested and supported by many laboratory experiments

The Primordial Soup Model

• Primordial soup: Earth’s oceans most likely were filled with various organic molecules
• Oparin and Haldane each hypothesized that these molecules formed spontaneously in chemical reactions energized by solar radiation, volcanic eruptions, and lightning

Oparin & Urey’s Hypothesis

• Earth’s early atmosphere: ↓ O 2 ; ↑N 2 , NH 3 , H 2 , H 2 O (g) , CH 4 ; ↑ Temp.
• Energy from lightning caused these gases to form simple organic compounds

Miller-Urey Experiment

• 1953 – experiment simulated early earth’s conditions based on Oparin & Urey’s hypothesis
• Procedures : chamber containing same gases (N 2 , CH 4 , H 2 , and NH 3 , H 2 O (g) ) ; electric sparks provided energy; ↓↓O 2 content; heated water (ocean)
• Results : over a few weeks, amino acids, fatty acids, & other hydrocarbons were created without human intervention
• Significance : amino acids make proteins; basic chemicals of life could have formed spontaneously under early Earth’s conditions
• Other experiments produced additional proteins, ATP, and nucleotides
• Atmosphere different?
• No ozone layer
• Would have destroyed NH 3 and CH 4 …don’t get the same molecules
• Where could the gases come from?
• Produced in ocean bubbles?
• Arose from deep sea vents?
• Still under investigation…

http://www.ucsd.tv/miller-urey/miller1.mpg

The Bubble Model

• Gases from underwater volcanoes trapped in bubbles (NH 3 , CH 4 , etc.)
• Chemical reactions occurred inside bubbles where the gases were shielded from UV radiation
• Organic molecules released into air when bubbles burst upon surfacing
• Simple organic molecules underwent further chemical reactions driven by UV radiation & lightning in atmosphere
• Complex organic molecules formed from additional chemical reactions carried by precipitation into oceans

Precursors of the First Cells

• RNA (ribonucleic acid) have been formed in the lab
• RNA assists in carrying out DNA’s instructions

Inorganic Molecules

RNA nucleotides

RNA macromolecules

RNA molecules catalyze protein synthesis

Self-replication

• Inorganic molecules can form RNA building blocks (NTs)
• RNA stores information like DNA
• RNA NTs combine to form larger RNA molecules
• RNA helps to make proteins (acts as an enzyme – catalyzes chemical reactions)
• Proteins carry out DNA’s cellular instructions
• RNA has the ability to copy itself
• RNA can mutate
• RNA could have been the first hereditary molecule in cells

Microspheres & Coacervates

• Cell-like structures form spontaneously from simple organic chemicals in the lab
• Microspheres = spherical structures made of amino acids (building blocks of protein) which form a membrane
• Coacervates = clusters of droplets made of different types of molecules ( e.g. a.a. & sugars)
• Both have life-like properties: engulf substances and enlarge – parts of cellular life not dictated by genes
• Microspheres could have been the first step toward cellular organization
• Not true cells without heredity

Origin of Heredity

• Most scientists agree that RNA probably evolved before DNA
• RNA can act as an enzyme
• Probably catalyzed formation of first proteins
• Perhaps some microspheres contained RNA
• RNA could be transferred to “offspring”
• Much, more to be learned…

12-2: The Evolution of �Cellular Life

The Evolution of Prokaryotes

• Fossil evidence is used to determine when the first organisms formed.
• Fossil = preserved/mineralized remains or imprint of a dead organism
• Form when an organism is covered by sediment and its tissues are eventually replaced by hard minerals
• Mold = type of fossil that is an imprint
• Cast = rock-like model of an organism created by the filling of a mold
• Oldest fossils are 2.5 billion years old
• Prokaryotes, see next slide
• Fossils show morphology, behavior, mode of locomotion

Fossilization Process

• Brachiopod dies and falls on the sea-bed. Organic remains: dispersed or eaten.
• Inorganic part (shell) is preserved. Worn down by erosion from water and sand.
• Sediments cover the shell. Process continues for millions of years. Sediments harden petrifying the shell.
• Fossil rises, through uplift & erosion, now being exposed to sun, the wind and the frost.

Prokaryotes, continued…

• Prokaryotes :
• Single-celled organisms
• No membrane-bound organelles ( e.g. mitochondria, chloroplasts)
• No nucleus (DNA floating)
• Cyanobacteria – some of the first prokaryotes seen in fossil record
• Photosynthetic, marine
• Added O 2 to the atmosphere over hundreds of millions of years…accumulated (21% today)

Two Groups of Prokaryotes

• Two groups of prokaryotes evolved:
• Eubacteria (AKA “bacteria”)
• Escherichia coli, Sulfolobus
• Contain peptidoglycan in cell walls
• Many cause disease & decay
• Archaebacteria
• Lack peptidoglycan in cell walls; have unique lipids in cell membranes
• Live in extreme environments: hot springs, deep sea vents, caves, etc.

The Evolution of Eukaryotes

• First eukaryotes appeared in fossil record ~1.5 billion years ago
• Larger than prokaryotes
• Complex internal membrane system
• DNA stored in a nucleus
• Specialized organelles:
• Mitochondria – organelle that carries out cellular respiration; make cellular energy
• Chloroplasts – organelle that carries out photosynthesis; in photosynthetic organisms
• Both are the size as prokaryotes
• Both contain their own DNA

The Origins of Mitochondria �and Chloroplasts

• Mitochondria & chloroplasts originated by the process of endosymbiosis (Margulis)
• Bacteria entered larger cells as undigested prey or parasites
• Continued to carry out photosynthesis or cellular respiration
• Host cell benefited from energy-producing mechanism; engulfed cell benefited from safe environment…mutualism!

Support for theory of endosymbiosis…

• Size & structure:
• Mitochondria & eubacteria ≈ same size; chloroplasts & cyanobacteria ≈ same size
• Both organelles surrounded by two membranes (from being engulfed)
• Smooth outer membrane resembles host cell’s organelle’s membrane
• Rough inner membrane resembles modern eubacteria
• Chloroplasts & cyanobacteria contain the same photosynthetic structures
• Genetic material:
• Mitochondria & chloroplast chromosomes are made of circular DNA like bacteria
• Genes on DNA of mitochondria & chloroplasts are different than those on DNA in nucleus
• Similar between bacteria and mitochondria & chloroplasts
• Reproduction:
• Mitochondria & chloroplasts reproduce in the same way as bacteria
• Binary fission (independent of host cell)

Multicellularity

• 6 Kingdoms of life
• 2 Prokaryotes:
• Eubacteria & Archaebacteria
• 4 Eukaryotes:
• Protists, Fungi, Plants, Animals
• Protists : large, diverse group of multicellular and unicellular organisms
• Paramecia , algae (seaweed), many human parasites, Amoeba , slime molds…

Trypanosoma

Trichomonas vaginalis

Dinoflagellate

• The Ciliophora ( ciliates ), a diverse protist group, is named for their use of cilia to move and feed.
• Plasmodium , the parasite that causes malaria, spends part of its life in mosquitoes and part in humans.
• Euglena , a single celled mixotrophic protist, can use chloroplasts to undergo photosynthesis if light is available or live as a heterotroph by absorbing organic nutrients from the environment.

DINOFLAGELLATE

Chrysophyta – golden algae

Brown Algae

Volvox and Green Algae

Slime Molds

Multicellularity, continued…

• Over time, some organisms evolved the trait of being multicellular (made up of at least two cells)
• Multicellularity allows an organism to have specific cells with specialized functions
• Cells for movement
• Cells for digestion
• Cells for vision
• Cells for disease prevention (immune)
• This is an advantage over a single-celled organism, whose cell must carry out all functions
• Oldest fossils of multicellular organisms are 700 million years old

Origins of Modern Organisms

• Most animal phyla evolved during the Precambrian era and Cambrian periods between 570-505 million years ago
• Known as the “Cambrian explosion” because of the rapid diversification of animals
• Animals that evolved during this time period most likely were the ancestors of all animals thereafter

Mass Extinctions

• ~440 m.y.a. the first mass extinction occurred…large % of all organisms went extinct (marks end of Ordovician period)
• Extinction: death of all members of a species
• Mass extinction: episode during which large numbers of species become extinct
• Mass extinctions are probably caused by changes in worldwide geologic and weather patterns
• Five mass extinctions have occurred during Earth’s history
• 6 th mass extinction underway
• Human activity is causing the destruction of fragile ecosystems
• Especially tropical rain forests
• ~1/2 the world’s tropical rain forests have already been lost
• Most the world’s biodiversity lives in tropical rain forests

12-3: Life Invaded the Land

The Ozone Layer

• Unsafe levels of UV radiation prevented the first organisms on Earth from leaving the oceans
• ~2.5 b.y.a. O 2 levels in the atmosphere began increasing
• Cyanobacteria were doing photosynthesis
• O 2 formed O 3 (ozone)
• Over millions of years, ozone was “thick” enough to protect organisms

Plants and Fungi on Land

• First land dwelling organisms:
• Fungi + plants or algae together
• Benefit one another:
• Plants make sugars from sunlight
• Fungi get minerals from rock
• Mycorrhizae : symbiotic (mutualistic) association between fungi and plant roots
• Mutualism : relationship between two species in which both benefit
• Plants and fungi began a terrestrial mutualism about 430 million years ago
• The evolution of land plants provided a food source for land-dwelling animals
• Arthropods were first animals to invade land (probably a scorpion-like animal)
• Arthropod: animal with hard outer skeleton, segmented body, and paired, jointed limbs
• Lobsters, crabs, insects, spiders
• Insects are most plentiful & diverse group…probably because of wings
• Search for food, mates, nesting sites
• Pollinators (flowering plant fossils 127 m.y. old)

Vertebrates

• Vertebrate: animal with a backbone
• Mammals, reptiles, fishes, birds, amphibians
• First vertebrates (on record) were small, jawless fishes, ocean-dwelling, 530 m.y.a.
• Jawed fishes evolved ~430 m.y.a.
• Bite & chew food…efficient predators
• Fishes are most successful living vertebrates
• Land-dwelling animals are descendants of fishes
• First vertebrates left the sea ~370 m.y.a.
• Amphibians:
• Smooth-skinned, four-legged animals
• Modern Ex: frogs, salamanders, toads, newts
• Moist breathing lungs could absorb O 2 from air (versus extracting it out of water)
• Evolution of rigid skeleton allowed:
• Support (base for limbs to work against)
• Reptiles evolved from amphibian ancestors about 340 m.y.a.
• Modern Ex: snakes, lizards, turtles, crocodiles
• Reptiles better suited for dry land than amphibians:
• Watertight skin (prevents moisture loss)
• Watertight egg (can lay egg on dry land)

Mammals & Birds

• Birds evolved from dinosaurs during/after the Jurassic
• Mammals evolved from therapsids during the Triassic
• Therapsids: reptiles w/ complex teeth & legs under their bodies

Mammals & Birds, continued…

• All dinosaurs but ancestors of birds went extinct 65 m.y.a.
• Climate became more moist, allowing birds & mammals to dominate
• Previously dry climate favored reptiles
• Continental drift: movement of Earth’s land masses over Earth’s surface through geologic time
• We find similar organisms on land masses that were once connected
• Marsupials in South America & Australia

Formation of Earth

Our planet began as part of a cloud of dust and gas. It has evolved into our home, which has an abundance of rocky landscapes, an atmosphere that supports life, and oceans filled with mysteries.

Chemistry, Earth Science, Astronomy, Geology

Manicouagan Crater

Asteroids were not only important in Earth's early formation, but have continued to shape our planet. A five-kilometer (three-mile) diameter asteroid is theorized to have formed the Manicouagan Crater about 215.5 million years ago.

We live on Earth’s hard, rocky surface, breathe the air that surrounds the planet , drink the water that falls from the sky, and eat the food that grows in the soil. But Earth did not always exist within this expansive universe, and it was not always a hospitable haven for life. Billions of years ago, Earth, along with the rest of our solar system, was entirely unrecognizable, existing only as an enormous cloud of dust and gas. Eventually, a mysterious occurrence—one that even the world’s foremost scientists have yet been unable to determine—created a disturbance in that dust cloud, setting forth a string of events that would lead to the formation of life as we know it. One common belief among scientists is that a distant star collapsed, creating a supernova explosion, which disrupted the dust cloud and caused it to pull together. This formed a spinning disc of gas and dust, known as a solar nebula . The faster the cloud spun, the more the dust and gas became concentrated at the center, further fueling the speed of the nebula . Over time, the gravity at the center of the cloud became so intense that hydrogen atoms began to move more rapidly and violently. The hydrogen protons began fusing, forming helium and releasing massive amounts of energy. This led to the formation of the star that is the center point of our solar system—the sun—roughly 4.6 billion years ago. Planet Formation The formation of the sun consumed more than 99 percent of the matter in the nebula . The remaining material began to coalesce into various masses. The cloud was still spinning, and clumps of matter continued to collide with others. Eventually, some of those clusters of matter grew large enough to maintain their own gravitational pull, which shaped them into the planets and dwarf planets that make up our solar system today. Earth is one of the four inner, terrestrial planets in our solar system. Just like the other inner planets —Mercury, Venus, and Mars—it is relatively small and rocky. Early in the history of the solar system, rocky material was the only substance that could exist so close to the Sun and withstand its heat. In Earth's Beginning At its beginning, Earth was unrecognizable from its modern form. At first, it was extremely hot, to the point that the planet likely consisted almost entirely of molten magma . Over the course of a few hundred million years, the planet began to cool and oceans of liquid water formed. Heavy elements began sinking past the oceans and magma toward the center of the planet . As this occurred, Earth became differentiated into layers, with the outermost layer being a solid covering of relatively lighter material while the denser, molten material sunk to the center. Scientists believe that Earth, like the other inner planets , came to its current state in three different stages. The first stage, described above, is known as accretion, or the formation of a planet from the existing particles within the solar system as they collided with each other to form larger and larger bodies. Scientists believe the next stage involved the collision of a proto planet with a very young planet Earth. This is thought to have occurred more than 4.5 billion years ago and may have resulted in the formation of Earth’s moon. The final stage of development saw the bombardment of the planet with asteroids . Earth’s early atmosphere was most likely composed of hydrogen and helium . As the planet changed, and the crust began to form, volcanic eruptions occurred frequently. These volcanoes pumped water vapor, ammonia, and carbon dioxide into the atmosphere around Earth. Slowly, the oceans began to take shape, and eventually, primitive life evolved in those oceans. Contributions from Asteroids Other events were occurring on our young planet at this time as well. It is believed that during the early formation of Earth, asteroids were continuously bombarding the planet , and could have been carrying with them an important source of water. Scientists believe the asteroids that slammed into Earth, the moon, and other inner planets contained a significant amount of water in their minerals, needed for the creation of life. It seems the asteroids , when they hit the surface of Earth at a great speed, shattered, leaving behind fragments of rock. Some suggest that nearly 30 percent of the water contained initially in the asteroids would have remained in the fragmented sections of rock on Earth, even after impact. A few hundred million years after this process—around 2.2 billion to 2.7 billion years ago—photosynthesizing bacteria evolved . They released oxygen into the atmosphere via photosynthesis and, in a few hundred million years, were able to change the composition of the atmosphere into what we have today. Our modern atmosphere is comprised of 78 percent nitrogen and 21 percent oxygen, among other gases, which enables it to support the many lives residing within it.

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The History of the Earth

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Presentation on theme: "The History of the Earth"— Presentation transcript:

Origin & Evolution of the Universe

Great Ideas in Science: Lecture 9 – Earth as a Planet Professor Robert Hazen UNIV 301 Great Idea: Earth, one of the planets that orbits the Sun, formed.

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1 Chapter 2 Creation of Oceans. 2 Supporting Evidence for the Big Bang Edwin Hubble discovered spreading of galaxies. Cosmic background radiation (the.

THE PRIMORDIAL EARTH Hadean and Archean Eons Solar System Includes: Sun Planets Moons Asteroids Comets.

Astro 10-Lecture 6: Formation and Structure of the Solar System What are the properties of the solar system? How are these properties explained by theories.

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The Origin of the Solar System

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Astronomy 100: Formation and Structure of the Solar System What are the properties of the solar system? How are these properties explained by theories.

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Comparative Planetology II: The Origin of Our Solar System.

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Earth Timeline: A Guide to Earth’s Geological History and Events [Infographic]

Earth’s Timeline and History

4,567,000,000 years ago, Earth was covered in molten lava. Earth was completely unrecognizable. In its earliest stage of formation, it was uninhabitable as it clumped from a cloud of dust .

About 1,000,000,000 years ago, Earth had its first signs of life. Single-celled organisms consumed the sun’s energy. As a waste product, these cyanobacteria eventually filled the oceans and atmosphere with oxygen.

Next, an oxygenated atmosphere paved the way for more complex life forms to exist. At about 100,000,000 years ago, dinosaurs roamed the Earth until their abrupt extinction.

Finally, 10,000,000 years ago was the age of mammals. And these mammals are our direct ancestors. It was only 100,000 years ago when homo sapiens truly evolved.

In this Earth timeline, we lay out all the pieces on the floor. What sequence of events has unfolded for Earth to support life and for it to evolve?

The Sculpting of Earth (4.6 – 4.0 billion years ago )

The Big Bang created all matter in the universe. This includes the sun, planets, and our solar system. At the center, the sun swept in smaller elements like hydrogen and helium. Farther away, heavier elements formed planets. Based on the core accretion model, gravity was the driver coalescing Earth from a cloud of dust.

In this early stage of Earth’s creation, the heaviest material like iron sank to the core . Lighter material remained on top to form a crust. Because the solid inner core heats the outer liquid layer, it produces convection currents. This geodynamo is Earth’s magnetic field . Without it, Earth would be blasted by harmful rays from the sun.

In the late Hadean Eon, the Earth was still in its late heavy bombardment stage . Earth was hit by asteroids, comets, and foreign objects left, right, and center. We know it wasn’t only Earth because we can see these impacts on other places in our solar system. Some scientists believe that water originated from the bombardment of comets at this time. In addition, there’s reason to believe that these collisions could have sparked the chemical building blocks for life – DNA .

One of the most important events for Earth was the formation of our moon. The giant impact hypothesis describes it as an object the size of Mars heading towards Earth at tremendous speed. After delivering a glancing blow to Earth, gravity pulls this object into orbit. Ever since this grande event in the Hadean Eon , it has remained in orbit ever since.

Earth Cooling and Primitive Life (4.0 – 2.5 billion years ago )

The collision of the moon into Earth significantly impacted climate, oceans, and life on Earth. Because the moon’s orbit drags Earth, it slowed Earth’s rotation significantly from 6-hour days to 24 hours. Having the moon in orbit also stabilized the Earth from wobbling. But most importantly, the collision of the moon tilted Earth on its axis . And because the Earth is tilted on its axis, Earth now had seasons.

Eventually, the climate on Earth became more stable in the Archean Eon . Instead of a molten state, the Earth started to cool down. Water vapor condensed to form oceans. And the Earth cooled down enough to create continents. Though opinions vary, “Vaalbara” became Earth’s first supercontinent .

As the Earth cooled down, a new form of life began to prosper. When oxygen was absent in the atmosphere , cyanobacteria could convert sunlight to energy. In shallow water, they metabolized their own food. As a waste product, cyanobacteria released oxygen into the oceans.

When oxygen mixed with iron in the oceans, rusted iron collected on the seafloor. The banded iron formation continued until there was no more iron in the oceans to rust. Oxygen had nowhere to go but into the atmosphere. That’s why this event is the Great Oxygenation Event .

An Oxygenated Atmosphere (2500 – 541 million years ago)

Earth now had an oxygenated atmosphere for new life to flourish on Earth. But it wasn’t cyanobacteria flourishing. Because oxygen was toxic for cyanobacteria, they poisoned all anaerobic life on Earth including themselves. Imagine a dominant species polluting the planet until extinction. The oxygen byproduct from cyanobacteria created an oxygen crisis on Earth.

At this time, methane was more abundant in the atmosphere. One thing that methane did very well was trap heat in the atmosphere. It’s one of the most efficient greenhouse gases there are. So when oxygen combined with methane, it produced carbon dioxide. All of a sudden, the greenhouse effect wasn’t as strong. As a result, the whole planet froze. It was “Snowball Earth” as the Earth went into an ice age for the next 300,000,000 years.

Another important consequence of an oxygen-filled atmosphere was the emergence of aerobic eukaryotes. Before the oxygenation, life was anaerobic. Eventually, aerobic respiration organisms emerged because of the enriched atmosphere. This increased the complexity of life. For example, multi-cellular organisms became apparent in this eon. But the abundance of CO 2 held eukaryotes from diversifying.

As oxygen filled the atmosphere, Earth’s ozone layer thickened. Before the presence of an ozone layer, life was restricted to shallow water. Because water shielded harmful radiation, that’s where life existed. Eventually, a thicker ozone layer (O 3 ) enabled life to diversify on land in the Proterozoic Eon .

The Cambrian Explosion and Fossil Records (541 – 245 million years ago)

The Cambrian explosion was the largest diversification of life in Earth’s history. Everything before this era was Precambrian. We couldn’t identify life because we didn’t have fossilized shells or animals . This is when hard-shelled invertebrates originated in the oceans. The Cambrian explosion started with the Age of Invertebrates. And life got more diverse from there.

Next came the Age of Fish when thousands of fish species arose. Then, the first vertebrate land animal made its leap ashore. Amphibians took a breath of fresh air and colonized the empty continent of Gondwana. This was the start of the Age of Amphibians. We share similar characteristics to our vertebrate ancestors . For example, humans have spines, jaws, and mouths originating from fish.

In the Paleozoic Era , lush rainforests flourished on land. But due to an abrupt shift in global warming, a major marine and terrestrial extinction event began. This event was the Carboniferous Rainforest Collapse. Plants and swamps were buried, compacted, and cooked into underground coal deposits . It left behind vast deserts for reptiles to eventually dominate the continental interior.

The Paleozoic Era ended with the largest extinction in Earth’s history. The Permian-Triassic Extinction vanquished 96% of all marine species. About 70% of terrestrial vertebrate species were wiped out. Opinions vary about the Permian-Triassic Extinction cause. But the consensus is that it was from a major asteroid impact event .

The Age of Reptiles and Dinosaurs (245 – 66 million years ago)

When Earth’s climate became hotter and drier, rainforests collapsed triggering the Age of Reptiles. Reptiles are different from amphibians because they lay their hard-shelled eggs on land. They essentially adapted to the land by cutting all ties with the ocean. Because reptiles evolved to dryland conditions , they gained a unique ecological advantage.

As conditions changed, dinosaurs (also known as terrible lizards) began to evolve. These reptile-like mammals had scaly skin and hatched eggs like reptiles. Some dinosaurs adapted as herbivores and some as carnivores. For the next 160 million years, dinosaurs were the dominant land vertebrates on Earth.

The Age of Conifers in the Mesozoic Era provided the spread of seeded plants. Conifers store vast amounts of carbon. As a result, oxygen content in the atmosphere jumped to 35% compared to 21% today. In addition, they provided habitat, shelter, and a source of food for specific animal species to survive.

Also notable is that Pangea existed as one supercontinent in this era. Dinosaurs lived on one supercontinent. Plate tectonics was the mechanism that eventually tore continents apart. Don’t forget that dinosaurs existed for 160 million years. So continental drift gradually rifted dinosaurs apart. We know this because we can find the same fossils on separate continents.

The Age of Mammals and Homo Sapiens (66 million years ago – now)

Ultimately, the start of the Cenozoic Era was the demise of dinosaurs. After a 6-mile wide asteroid hit Earth, a dust cloud blocked the sun. This caused temperatures to plummet which was the heart of the damage from the Cretaceous–Paleogene extinction event. Because of the worldwide climate disruption, it was responsible for the extinction of the dinosaurs.

Mammals existed long before the Cenozoic Era. But they kept a low profile because dinosaurs dominated the land. The extinction of the dinosaurs marked the Age of Mammals. When dinosaurs roamed the Earth, mammals remained small and furry. And because dinosaurs went extinct, mammals emerged as the largest land animals at this time.

Apes remained in trees for their primary food source. Eventually, grass began to spread in places like the African Savannah and there were fewer trees. This forced apes to walk to new food sources. With their heads above the grass to see predators, apes evolved by walking on two legs. It also helped to have their hands available when they were traveling.

As the timeline to modern human evolution begins, hominids were the early proto-humans. They were known for sharpening objects with silicon rocks. They began to master the use of their hands and fingers. In the Stone Age, early humans had fire under control. This enabled them to cook their food giving them more calories. Modern humans learned to make more complex sounds and share information in groups. So humans have only existed for about 0.004% of the age of the Earth.

Geologic time is vast

It’s almost unimaginable the story of Earth. It spans over 4.5 billion years.

Scientists are still fitting all the pieces to the puzzle.

Since its creation, oceans, continents, and life as we know it has remarkably transformed. Life has evolved and adapted.

This article assembles some of the key events. From evolution to extinction, these are events that have unfolded as part of the Earth timeline. Though opinions vary, we’ve leaped through 4.5 billion years of Earth’s history and provided a general guideline.

A Guide to Earth’s Geological History and Events

Earth is a constantly changing planet. Each era has its own unique geological history and events.

Earth’s geological history will be of interest to students, professionals, and enthusiasts of earth science.

Now, it’s time to let you take the stage. What are some important events we missed? Please let us know with a comment below.

How Does the Supercontinent Cycle Work?

Metamorphic Rocks: Heat, Pressure and Metamorphism

How Was the Grand Canyon Formed?

Pacific Plate: Movement and Direction of the Pacific Tectonic Boundary

What Are the 3 Types of Rocks?

Mountain Building: How Mountains are Made

Plate Tectonic Types: Divergent, Convergent and Transform Plates

Soil Nutrients Deficiency and Replenishing

Eurasian Plate: Tectonic Boundary and Movement

What is a Stratovolcano (Composite Cone)?

Banded Iron Formation (BIF): How These Rocks Got Their Stripes

Inside Earth: The Crust, Mantle and Core

Chemical Weathering: Hydrolysis, Oxidation and Acidic Reactions

Transform Plate Boundaries: Sliding Plate Tectonics

39 comments.

Hi W. These are 2 separate topics of themselves. I’ve decided to break the “Big Bang” and “Human Evolution” into separate posts. My post on human evolution is not as comprehensive for covering appendages and organs (eyes, ears, etc.). But I think my article on the Big Bang is pretty detailed. Here they are:

• The History of the Universe: The Big Bang and Beyond – https://earthhow.com/history-of-the-universe/
• Human Evolution: A Timeline of Early Hominids – https://earthhow.com/human-evolution-timeline/
• Theory of Evolution: Charles Darwin and Natural Selection – https://earthhow.com/theory-of-evolution/

Very disappointing. Leaves much to be desired and explains nothing about how any species evolved simultaneous breeding PAIRS, not to mention how development could focus on appendages and organs (eyes, ears, etc.) for which no “simple” organism could know existed before such development. And, of course, it fails to explain from where the elements to cause the “big bang” came. It’s a nice hypothesis, but it has less proof and more holes than an intelligent-design theory.

Do not need to have any typo’s in your writing.

esta bonita la historia

Life is born newly every second. Same time life is dying every second

As per our Hindu Vedas we have 33,000,000 million species on our earth. So we human beings are also changing like our mobile phones. Finally all is like a dream.

This is cute, watching people fight over the idea that they know any “facts ” about the universe. It’s quite literally beyond the comprehension of a human brain. We aren’t able to understand the size, how it started or even the most basic principles, yet you are arguing as if you understand any part of it.

It’s like watching fruit flys fight over 401ks. Guys, seriously. You simply don’t know the first thing about anything yet.

What an incredibly accurate and detailed piece! You broke it down layer by layer and it really helped making sense of things I previously hadn’t known.

Great article. Good work.

The Big Bang did not create our solar system. It happened approx 13-14 billion years ago; our sun and solar system formed 9 billion years later. Our sun is only about 4.6 billion years old. It is described as a “third-generation star”. The Big Bang created all matter in the universe but that matter was not in the form it is now – for example none of the heavy metals like iron, gold, carbon, etc existed then (what we and our planet are made out of) those elements were all formed later by reactions within the first generations of stars.

I found this article very interesting.

I think there is a typo in the “age of dinosaurs” section. Should be “reptile-like animals”, not “reptile-like mammals”. Dinosaurs were reptiles, not mammals.

Dinosaur Pictures is an interactive map that lets you see how the Earth looked like up to 750 million years ago.

Do have like a map of the earth through out the history.

That’s a wonderful history of earth

Please check your six eras legends are mixed.

This is very helpful

We can write a thousand page book in fine print and miss one or even ten specific things that one may search for, its only natural.

And the topic is nature by the way

Wow this really does help!!

Can you please give us your references?

it was amazing and very helpful.

What seems to be missing is the actual geological changes in the earth’s surface that gave rise to the different land masses and bodies of water.

Worst case: “Since about 1,000,000,000 years ago, Earth had its first signs of life.” NOT! Life emerged at approximately 4.4 BYA. No excuse, guys! Very inaccurate science. Dates are WAY off on numerous topics. DK

Very helpful charts look amazing thanks for writing this

This was really helpful 👍🏾

The Permian-Triassic mass extinction was NOT due to a meteorite impact. Consensus is that it was due to the eruption of the Siberian Steps. There is overwhelming evidence that the Siberian Traps erupted continuously for approximately 1 million years, emitting trillions of tons of CO2 into the atmosphere, disrupting the carbon cycle and causing a greenhouse gas climate catastrophe which warmed the oceans, which in turn caused methane hydrates at the bottom of the ocean to melt and release methane into the atmosphere.

What seems to be missing is the main discussion of geology of the earth, which is about the rocks and physical processes that formed them. What is not missing is a long discussion of the supposed evolution of biological creatures.

A volcanic event was to have occurred in what is now Siberia around 250 million years ago that wiped out the plants and herbivores that per-existed dinosaurs. Fossil evidence is said to exist of these herbivores. The event is to have spewed out enough lava to cover the entire USA 1000 ft deep, along with noxious particulates, sulfurous gases and co2 that changed the climate. The acid gases poisoned the seas resulting in massive extinctions.

Nice summary, thank you. I am, however, a bit puzzled that you refer to dinosaurs as (reptile-like) mammals. Are you sure they were mammals?

I have throughly enjoyed reading this work. It has simplified processes of which I was unsure. Thank you for all the work that you have put in to enable me to be able understand the geological history of the planet upon which I live.

In the second paragraph of the Cenozoic Era, it says”When dinosaurs roamed the Earth, mammals remained small and fury.” It should say small and furry, not fury.

By the way, despite the minor errors I’ve pointed out, this is an excellent summary.

While the meteor that hit what is now present day Yucatan wiped out ALMOST all dinosaurs, especially the large ones, the avian dinosaurs survived and gave rise to modern birds. I mention this because you say in the first paragraph of the section on the Cenozoic Era that the dinosaurs went extinct. My point is, that they didn’t ALL go extinct, as previously thought.

In the second paragraph in the Mesozoic era section you say “As conditions changed, dinosaurs (also known as terrible lizards) began to evolve. These reptile-like mammals had scaly skin and hatched eggs like reptiles.” While there may have been a common ancestor to dinosaurs and mammals, I’m pretty sure there were no mammals at this point.

In a PBS video it said that Pangea had formed during the Paleozoic, not the Mesozoic.

Hi, nice write up, however, I noticed the color coding of the bar graph and the corresponding era isn’t matching at the very top of the page.

It doesn’t say anything about the major types of plants in the Mesozoic era like conifers and gingkos

Great synopsis and very helpful to my home-schooled children. I would suggest a modification to the presentation of the giant impact hypothesis. The hypothesis promotes that Mars-sized body, known as Theia, collided with Earth, throwing vaporized chunks of the earth’s crust into space (as opposed to delivering a glancing blow, implying that Theia survived and is now the moon). Gravity bound the ejected particles together, creating the moon. The idea is supported by the similarities in composition of earth and moon matter. Thank you.

Very Helpful for my class project! Thank you so much!

Thanks, fixed it

Hello Your first paragraph has a typo………..”In its earliest stage of formation, it was inhabitable as it clumped from a cloud of dust” ”inhabitable” obviously should be ”uninhabitable” Regards Mike

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If you like geology and the history of the Earth, or if you are a teacher and need to explain this topic to your students, we are sure that this infographics template will be more than interesting for you. In it you will find illustrations with which you can explain the different layers that form the Earth, tables in which you can compare the different eras, graphs and diagrams to show data and timelines. These and many other resources are waiting for you in this template, so download it and become an expert in geology.

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Our History

Every year on april 22, earth day marks the anniversary of the birth of the modern environmental movement in 1970. let’s take a look at the last half-century of mobilization for action:.

THE ORIGINS OF EARTH DAY

In the decades leading up to the first, americans were consuming vast amounts of leaded gas through massive and inefficient automobiles. industry belched out smoke and sludge with little fear of the consequences from either the law or bad press. air pollution was commonly accepted as the smell of prosperity. until this point, mainstream america remained largely oblivious to environmental concerns and how a polluted environment threatens human health., however, the stage was set for change with the publication of rachel carson’s new york times bestseller silent spring in 1962. the book represented a watershed moment, selling more than 500,000 copies in 24 countries as it raised public awareness and concern for living organisms, the environment and the inextricable links between pollution and public health., more on gaylord nelson and denis hayes, the idea for the first earth day, senator gaylord nelson, the junior senator from wisconsin, had long been concerned about the deteriorating environment in the united states. then in january 1969, he and many others witnessed the ravages of a massive oil spill in santa barbara, california. inspired by the student anti-war movement, senator nelson wanted to infuse the energy of student anti-war protests with an emerging public consciousness about air and water pollution. senator nelson announced the idea for a teach-in on college campuses to the national media, and persuaded pete mccloskey, a conservation-minded republican congressman, to serve as his co-chair..

Senator Gaylord Nelson recruited Denis Hayes, a young activist, to organize the campus teach-ins and to scale the idea to a broader public, and they choose April 22, a weekday falling between Spring Break and Final Exams, to maximize the greatest student participation.

Recognizing its potential to inspire all americans, hayes built a national staff of 85 to promote events across the land and the effort soon broadened to include a wide range of organizations, faith groups, and others.  they changed the name to earth day, which immediately sparked national media attention, and caught on across the country.  earth day inspired 20 million americans — at the time, 10% of the total population of the united states — to take to the streets, parks and auditoriums to demonstrate against the impacts of 150 years of industrial development which had left a growing legacy of serious human health impacts. .

Groups that had been fighting individually against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, freeways, the loss of wilderness and the extinction of wildlife united on Earth Day around these shared common values. Earth Day 1970 achieved a rare political alignment, enlisting support from Republicans and Democrats, rich and poor, urban dwellers and farmers, business and labor leaders.

By the end of 1970, the first earth day led to the creation of the united states environmental protection agency and the passage of other first-of-their-kind environmental laws, including the national environmental education act, the occupational safety and health act, and the clean air act. two years later congress passed the clean water act., the dawn of the modern environmental movement. earth day 1970 became, and continues to be to this day, the largest secular day of protest in the world..

The principal Earth Day event in 1980, held in Washington. D.C. across from the White House, capped a decade of substantial US environmental legislation, including the Endangered Species Act, Marine Mammal Protection Act, Superfund, Toxics Substances Control Act, the Resource Conservation and Recovery Act, and of course the Clean Air Act and Clean Water Act. It had seen the creation of the Environmental Protection Agency and the banning of DDT and of lead in gasoline. Earth Day continued to expand internationally during the 80’s, as did international policy initiatives.

As 1990 approached, a group of environmental leaders approached denis hayes to once again organize another major campaign for the planet. this time, earth day went truly global, mobilizing 200 million people in 141 countries and lifting environmental issues onto the world stage. earth day 1990 gave a huge boost to recycling efforts worldwide and helped pave the way for the 1992 united nations earth summit in rio de janeiro. it also prompted president bill clinton to award senator nelson the presidential medal of freedom — the highest honor given to civilians in the united states — for his role as earth day founder..

As the millennium approached, Hayes agreed to spearhead another campaign, this time focusing on global warming and pushing for clean energy. Earth Day 2000 combined the big-picture feistiness of the first Earth Day with the international grassroots activism of Earth Day 1990. Earth Day had the internet to help link activists around the world. By the time April 22 came around, 5,000 environmental groups worldwide were on board, reaching out to hundreds of millions of people in a record 184 countries. Events varied: A talking drum chain traveled from village to village in Gabon, Africa, for example, while groups of thousands and more gathered worldwide for various events, rallies, and marches.

Nearly one billion people around the world took action for the 40th anniversary of earth day. an estimated 20,000 partners took action on climate change and other environmental issues through climate rallies, billion acts of green™, and by engaging civil leaders in plans to build a green economy, connected through the online action center at earthday.org. through the global day of conversation, more than 200 elected officials in more than 39 countries took part in active dialogues with their constituents about their efforts to create sustainable green economies and reduce their carbon footprints..

Signing of the Paris Agreement. It was no accident that the United Nations selected Earth Day to sign the most significant climate accord in the history of the climate and environmental movement. On Earth Day 2016, world leaders from 175 nations broke a record by doing exactly that.

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History of the Earth

Nov 19, 2014

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History of the Earth. Ch 14. Chapter 14 Vocabulary :. 1. Fossil 2. Law of superposition 3. Radiometric dating 4. Spontaneous generation 5. Biogenesis 6. endosymbiont theory.

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• time period
• paleozoic era
• mesozoic era
• cretaceous time period
• major geological event occurred

Presentation Transcript

History of the Earth Ch 14

Chapter 14 Vocabulary: • 1. Fossil • 2. Law of superposition • 3. Radiometric dating • 4. Spontaneous generation • 5. Biogenesis • 6. endosymbiont theory

SC.912.L.15.1Ch 14 Explain how the scientific theory of evolution is supported by the fossil record, comparative anatomy, comparative embryology, biogeography, molecular biology, and observed evolutionary change.

How Did Life Begin? The Earth formed about 4.6 billion years ago according to evidence obtained by radiometric dating.

The age of the rocks and the fossils in them can be determined by the position and the amount of radioactive material in the rocks. • Law of superposition

Radiometric Dating or ½ life

½ life • Compare it to the amount of time it takes for ½ of the carbonation in this bottle to leave… if we know how much time it takes, we could calculate the age of the bottle of soda based on how much carbonation was left in the container.

Radiometric dating • Gives a numerical age • Places rocks and fossils in a time period • Uses isotopes that decay at a constant rate • Uses isotopes that decay very slowly/ have a long ½ life.

fossil • A fossil is any preserved evidence of an organism. • They form best in sedimentary rocks • They can be evidence or an organism, like foot prints or actual remains.

What do fossils tell us and how do we know how old they are? The fossils in the bottom layer of rock are older

Fossils show evidence of change in organisms, what types of organisms lived in each time period and that the complexity has increased over time. • We know how old they are by relative positions and radiometric dating.

Law of superposition! • Youngest are on the top • Oldest are on the bottom • unless they have been disturbed!

The geologic time scale • is a model of the history of Earth showing the major events that occurred along the way.

The longest units of time are eons and include the Precambrian time and Phanerozoic. • The second largest unit of time is called an era and includes the Precambrian, Paleozoic, Mesozoic and Cenozoic. • Each era can be divided into parts called periods and periods may be divided into the smallest parts called epochs.

The history of the earth is broken up into a set of divisions for describing geologic time. • the generally accepted divisions are • eon • era • period • epoch • age

PRECAMBRIAN • SO LONG AGO… • We know little due to deformation of rock layers. • Large areas of Precambrian rock exposed are called shields. North America’s is called the Canadian shield.

Precambrian life • Fossils are rare • Simple organisms with soft bodies • Volcanic activity heat and pressure “erased” the fossil evidence. • Stromatolites blue-green algae were common.

14. Sum up what events occurred in Precambrian time. Makes up almost 90% of Earth’s history, earth formed, first life appeared, autotrophs released oxygen into the atmosphere, Eukaryotes developed. At the end the first animals developed. Simple animals lived in the oceans

Paleozoic Era

Paleozoic Era: Life • trilobites Brachiopods are marine animals that, upon first glance, look like clams

Paleozoic • Lots of fossils • Trilobites index fossil • Invertebrates, worms, jellyfish, snails vertebrates appear • Fish, amphibians • Insects • Reptiles • .

15. Sum up the Paleozoic Era. Explosion of life! Fish, land plants and insects appeared. First tetrapods or land vertebrates appeared reptiles arrived at the end of the Paleozoic

Mesozoic Era

Mesozoic Erathe age of the reptiles

Dinosaurs and other archosaurs, such as the pterosaurs, dominated the land biota. . .

17. Sum up the Mesozoic era. Mammals and dinosaurs appeared. Flowering plants, birds evolved from dinosaurs. The age of the reptiles

Impact theory • No dinosaurs found after the cretaceous- tertiary • What happened? • Possible impact hypothesis

18. What makes scientists think a meteor hit the earth during the cretaceous time period? There is iridium found in the rock layers called the KT boundary. Iridium is found mostly in objects from space, like a meteor.

19. How might a meteor impact cause a mass extinction? The debris could cause global climate changes

20. What other major geological event occurred during the Mesozoic era? Pangaea the single land mass moved so that the continents were roughly in their current position by the end of the Mesozoic era.

Cenozoic Age of the Mammals

Cenozoic • The continents moved to their current positions. • Alps Himalayas formed • Small rodents, early horse, and bats • Ice cap formed • Land bridges formed Ice age • Early ancestors to humans fossils found

21. What is the most recent era? The Cenozoic era • 22. What are the most dominant organisms in the Cenozoic era? Mammals • 23. When did humans arrive on earth? at the very end of the time scale

What life do we associate as occurring during the Mesozoic era? • Dinosaurs

How do we think the extinction of the dinosaurs happened? • giant asteroid hit earth

Humans and large mammals appeared in the Era called what? • Cenozoic

Section 2 The Origin Of Life • 4. Spontaneous generation • 5. Biogenesis • 6. endosymbiont theory

What were the conditions of early Earth like?

Hot, meteorites, volcanoes .Minerals in the oldest known rocks suggest that the earth’s atmosphere had little or no oxygen

The primordial soup model and the bubble model propose explanations of the origin of the chemicals of life. Scientists think RNA formed before DNA or proteins formed.

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