Earth History

Geologic Time Scale

Geologic Time Scale

• The geologic Time Scale is a record of Earth’s history– The Earth is 4.6 Billion Years Old

• The names of the divisions do not change however the years designating the beginning and end of these divisions are often reconsidered

Eons

• The time scale is divided into eons• An Eon is the longest time unit and is

measured in billions of years

Eons

• The history of the Earth is divided into 4 eons:–Hadeon(4.6 Bya-3.8 Bya)–Archaen(3.8 Bya-2.5 Bya)–Proterozoic(2.5 Bya-542 mya)–Phanerozoic(542 mya-Present)

Precambrian

• The Precambrian includes the – Hadeon – Archaen – Proterozoic eons.

• Includes 90% of Earth’s History• The end of the Proterozoic is defined by

the first appearance of organisms with hard parts(shells, skeletons)

Precambrian

• Up until the end of the Proterozoic all organisms had soft bodies

• Many of these organisms resemble:– Sponges– Snails – Worms

Eras

• Eras are the next longest span of time. • Eras are measured in hundreds of millions

of years

Eras

• The names of the eras of the Phanerozoic are based on their age– “Paleo” means old– “Meso” means middle– “Ceno” means recent– “Zoic” means life

Eras

• The Phanerozoic Eon is divided into 3 Eras:– Paleozoic(542 mya-250 mya)– Mesozoic(250 mya-65 mya)– Cenozoic(65 mya-Present)

Paleozoic Era

• During the Paleozoic era the oceans had a wide diversity of plants and animals

• Trilobites were the dominant organism in the oceans during the early Paleozoic

• All trilobites were extinct by the end of the Paleozoic

Paleozoic Era

• Land plants and land animals first appeared

• At the end of the Paleozoic 90% of marine organisms went extinct

• This is considered to be the largest mass extinction event in Earth’s History

Mesozoic Era

• The mesozoic era is known for:– The emergence of the dinosaurs– Reef Building corals– Predatory reptiles– Amphibians living on land and in water

• Dinosaur population began to decline towards the end and mammals began to evolve

Mesozoic Era

• Like the Paleozoic the end of the Mesozoic is marked by a massive extinction event

Cenozoic Era

• During the Cenozoic:– Mammals increased in number and diversity– Human ancestors developed– Grasses and flowering plants expanded on

land– Ocean life remained relatively unchanged

however

Periods

• Eras are divided into periods• Periods are usually defined by life forms

that appeared or went extinct during that time

• Some periods are named for a geographic area in which the first rock of that age was discovered

Periods

• The Mississippian period was named for a distinctive limestone that formed along the Mississippi River

Periods

• The Jurassic Period is named for the rocks discovered in the Jura Mountains in Europe

Epochs

• Periods are divided into Epochs which are measured in millions of years to tens of millions of years

• The fossil record the Cenozoic Era is relatively complete

• There has been less time for weathering and erosion to destroy the fossil record

Epochs

• Certain organisms are used to distinguish the various epochs – Marine Fossils are used to mark the

Oligocene– Terrestrial plant fossils are used to mark the

Eocene

Relative Dating

Relative Dating Of Rocks

• Relative Dating estimates the order of past geologic events by using basic stratigraphic rules

• Relative dating does not give us the ages of past events but can tell us the order in which they happened

Relative Dating

• Uniformitarianism states that “The Present is the Key to the past”.

• In other words processes that are occurring today were more than likely occurring throughout Earth’s history

Geologic Principles

• Principle of Superposition• Principle of Original Horizontality• Principle of Cross Cutting Relationships

Principle of Superposition

• The principle of superposition states that in an undisturbed rock sequence the oldest rocks are on the bottom and going up they progressively get younger

• faculty.icc.edu/easc111lab/labs/labf/prelab_f.htm

• Remove frame 

Principle Of Original Horizontality

• The Principle of Original Horizontality states that sedimentary rocks are deposited in horizontal or nearly horizontal layers

Principle Of Original Horizontality

• If the layers are not horizontal then there was an event that caused the layers to fold or tilt

Principle Of Cross Cutting Relationships

• The Principle of Cross Cutting Relationships states that a rock that intrudes into another rock is going to be younger than the rock that it is cutting into

Principle Of Cross Cutting Relationships

• The Principle of Cross Cutting Relationships allows us to say that the fault formed after the rock layers formed

• A fault is always going to be younger than the feature that it cuts through because of the Principle of Cross Cutting Relationships

Inclusions

• Inclusions are pieces of one rock that are contained within another

• If a rock layer contains particles of another rock material from the layer beneath it then the layer beneath it is older

Inclusions

• The bottom layer became eroded and the loose material became incorporated in the new top layer

• A newly formed rock that is Jurassic in age may contain particles that are Ordovician in age

Unconformities

• Erosion and flooding can often destroy evidence of past geologic events

• Erosional surfaces may be later buried by a younger rock

• When a buried erosional surface results in a gap in the rock record it is called an unconformity

Unconformities

• There are 3 types of unconformities:– Disconformity– Nonconformity– Angular Unconformity

Disconformities

• A disconformity is an unconformity between parallel layers of sedimentary rock which represent a period of erosion or non-deposition

Nonconformities

• A nonconformity is a break that separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks

Angular Unconformity

• An angular unconformity consists of a tilted sedimentary rock that is overlain by a younger more flat lying strata

Correlation

• Correlation is the matching of outcrops of one geographic region to another

Absolute Dating

Absolute Dating Techniques

• Absolute dating allows scientists to determine the actual age of a rock, fossil or other object

• Scientists use radioactive decay to determine the ages of rocks

Radioactive Decay

• Radioactive substances emit particles at a set rate

• As they emit particles the number of protons and neutrons change and the element is converted into a different element

• Radioactive dating is the emission of radioactive particles and the resulting change into other elements

Radiometric Dating

• Radiometric dating is the process in which scientists determine the ratio of parent nuclei to daughter nuclei

• After they determine the ratio of parent to daughter nuclei they can figure out the actual age of the object

Radiometric dating

• As this process takes place the “Parent” decays into the “daughter”

• The parent isotope is what the element originally was

• The daughter isotope is what the parent isotope is turning into

Radiometric Dating

• Example:– Uranium-238 will decay into Lead-206 during

a specific span of time• The rate at which these particles decay

remains constant making them good indicators of the actual age of the object

Half Life

• Half life-The period of time it takes for one half of the isotope to decay

Useful IsotopesRadioactive Isotope (Parent)

Approximate Half Life Decay Product (Daughter)

Rubidium-87 48.6 Billion Years Strontium-87

Thorium-232 14 Billion Years Lead 208

Potassium 40 1.3 Billion Years Argon 40

Uranium 238 4.5 Billion Years Lead 206

Uranium 235 700 Million Years Lead 207

Carbon 14 5730 Years Nitrogen 14

Useful Isotopes

• Carbon 14-Useful for finding the age of materials that are of organic origin– Amber– Humanoid Bones– Papyrus– Charcoal Fragments

• The half life of Carbon 14 is 5730 therefore it would be used to date rocks that are thousands of years old

Half Lives

Number Of Half Lives

Percent Parent Isotope

Percent Daughter Isotope

Elapsed Years

0 100% 0% 0

1 50% 50% 5730

2 25% 75% 11560 (5730 X 2)

3 12.5% 87.5% 17090(5730 X 3)

Half Lives

• The half life of U-238 is 4.5 Billion Years old so therefore it would not be useful to date something that is thousands of years old

• The isotope used is based on the age range of the rock

Practice

• How old are the following rocks:– Contains 50% U-235, 50% Pb-207– Contains 25% K-40, 75% Ar-40– Contains 12.5% C-14, 87.5% N-14– Contains 50% U-238, 50% Pb-206

Other Absolute Dating Techniques

• Dendrochronology-The science of comparing annual growth rings in trees to date event and changes in the past environments

• During the spring a tree experiences it’s greatest growth

• During the winter it’s growth is less

Dendrochronology

• The widths of a trees rings are related to the climate conditions during growth periods

Varves

• Vares are bands of alternating light and dark colored sediments of sand, clay and silt

• During the Pleistocene

(11,000 years ago) there was mass glaciation• When the glaciers melted the glacial sediments were

deposited in lakes

Varves

• The glacier sediment is dark in color • When they mix with sediments that

accumulated during warm temperatures varves are formed

Key Beds

• Key Beds-Sediment layers that serves as a time marker in the rock record.

• Key beds result from:– Volcanic Ash– Meteorite Impact debris

• Found in rocks deposited during the Cretaceous Period

Key Beds

• Key Beds are released by volcanic eruptions as well

• Will be used to date rocks back to the eruption of Mount St. Helens(1980)

Fossils: Indicators Of Past Life

Fossils

• Fossils are remains or traces of prehistoric life

• Fossils are important tools in interpreting the geologic past

Fossils

• Fossils are important in:– Providing evidence that organisms have

changed through time– Providing information about past

environmental conditions– Useful in correlating rock layers

Fossils

• The following is a trilobite. A useful fossil for dating back to the Cambrian period

Fossils

• A fossil is said to have original preservation if the remains have not undergone any change

• These fossils require conditions such as:– Freezing– Drying Out– Oxygen Free Environments

Fossils

• Some environments that can provide original preservation are:– Permafrost in Alaska– Sticky ooze in La Brea Tar Pits in California– Tree sap that hardens into amber

Altered Hard Parts

• Altered hard parts are fossils whose organic material has been removed

• Permineralization is the process by which minerals fill in the empty pore spaces

• Petrified Wood

Index Fossils

• Index Fossils are remains of plants or animals that can be used by geologists to:– Correlate rock layers over large areas– Date a particular rock layer

Index Fossils

• Index Fossils must be:– Easily Identifiable– Widespread Geographically– Short Time Range

Index Fossils

• Mollusk Ecphora-Excellent index fossils for the Mesozoic era.

• It has a: – Distinct Shape– Widespread Abundance

Molds

• A mold is formed when a shell or other structure is buried in sediment and then dissolved by underground water

• If the mold later becomes filled with minerals it is known as a cast

Trace Fossils

• Trace fossils are evidence of an animals past activity

• Trace fossils include:– Footprints– Worm Trails– Burrows

Trace Fossils

• Dinosaur track ways in Texas and Connecticut

• Gastroliths-Rocks that dinosaurs had in their stomachs. Helped them digest their food

• Caprolites-Remains of solid waste material. Helps us learn about eating habits

Fossils

• Fossils have helped scientists determine:– How organisms have changed through time– Early environmental conditions– Past patterns and cycles than can help predict

future climate changes

The Precambrian Earth

The Precambrian Earth

• The Precambrian includes the:– Hadeon Eon(4.6 Ga-3.8 Ga)– Archaen Eon(3.8 Ga-2.5 Ga)– Proterozoic Eon(2.5 Ga-542 mya)

Earth’s Birth

• The Earth must be at least as old as the oldest rocks.

• The oldest rocks are around 3.9 Billion years old

• Rocks older than this have been eroded

How Old Is The Earth?

• Scientists Agree that the Earth is about 4.6 Billion Years old due to meteorites found that date back to 4.6 Billion Years

Heat Sources

• It is believed that the Earth was very hot when it first formed

• Earth’s heat sources destroyed much of the evidence for this time period

Formation Of The Crust

• Iron and Nickel melted and concentrated into the core due to their high densities

• Granite, a less dense material composes the crust

• Denser minerals compose the mantles

Differentiation

• Differentiation is the process where the heavier materials sink towards the center and lighter materials accumulate towards the surface

Formation Of The Crust

• The formation of the crust is believed to have been completed about 2.5 Billion Years ago (The boundary between the Archaen and the Proterozoic Eons)

Growth Of The Continents

• By 1.8 Ga Laurentia formed• Laurentia is an ancient continent that was

composed of most of modern day North America

Grenville Orogeny

• 1.8-1.6 Ga-The Grenville Orogeny• The Grenville Orogeny was a collision of

Laurentia with an Island Arc• By the end of the Proterozoic 75% of

North America had formed

Rodinia

• During the Proterozoic all land came together to form a supercontinent known as Rodinia which broke apart during the Early Phanerozoic

Earth’s Early Atmosphere

• Hydrogen and Helium composed Earth’s Early Atmosphere

• These gases escaped while more massive gasses such as Nitrogen and CO2 did not

• Massive volcanic activity released gases such as H2O, CO2, N2, and CO which is believed to have formed Earth’s early atmosphere

Cyanobacteria

• Stromatolites are mounds of billions of cyanobacteria

• Cyanobacteria are oxygen producing bacteria

Stromatolites

• Stromatolites formed:– During the Proterozoic– In Shallow oceans

BIF’s

• BIFs(Banded Iron Formations) are deposits which consist of alternating bands of chert and iron oxides

• BIF’s formed from 2.5 Ga-1.8 Ga

BIF’s

• BIF’s were formed by Stromatolites which were giving off Oxygen in shallow marine environments

• BIF’s stopped forming when Oxygen levels rose

Red Beds

• Red Beds are sedimentary rock deposits that contain oxidized iron

• Red Beds are evidence that the Proterozoic contained oxygen

Formation of the Oceans

• As the Earth cooled the Water Vapor in the air condensed and liquefied

• The water filled the low lying, basalt floored basins

• Another hypothesis suggests that Earth’s water came from comets made of frozen gas and water

Proterozoic Life

• It is believed that the only life forms that existed during the Proterozoic were Prokaryotes– Prokaryotes are single celled organisms. They

have no nucleus– Eukaryotes are organisms that are composed

of cells that contain a nucleus

Snowball Earth

• 800-700 mya it is believed that there was a widespread glaciation called “Snowball Earth”

• Glaciers extended all the way down to the equator

The Paleozoic Era

Periods Of The Paleozoic

• Cambrian• Ordovician• Silurian• Devonian• Carboniferous

– Mississippian– Pennsylvanian

• Permian• The Paleozoic runs from 542 mya-250 mya

Paleozoic

• The Paleozoic Era lasted from 542 mya to 250 mya

• By the Cambrian Laurentia had split off from Rodinia– Was located near the equator– Surrounded by tropical seas

Change In Sea Level

• A transgression is a rise in sea level• A regression is a fall in sea level

Sea Level

The Grand Canyon shows the sandstone-shale-limestone deposits of the Cambrian

Sea Level

• The sandstone-shale-limestone sequence was deposited side by side however were found stacked one on top of the other in the grand canyon

• This was due to a change in sea level

Cambrian Explosion

• The Cambrian Explosion in an increase in diversity and abundance of life forms at the beginning of the Cambrian Period

• The beginning of the development of hard parts such as skeletons mark the beginning of the Cambrian

• Trilobites are a very good index fossil for the Cambrian

Middle Paleozoic

• Sea Level rose during the Ordovician

• In the middle Ordovician Corals and sponges became common. Began to build reefs

• Reefs protect the environments behind them from wave energy

• The area behind a reefs is called a Lagoon

Landmasses

• Baltica-Consisted of modern day Northern Europe and Russia

• Laurentia-Most of Present Day North America

• Avalonia-Present day Newfoundland

Taconic Orogeny

• The Taconic orogeny was a collision between Laurentia and an Island arc

• Occurred in the Middle Ordovician• Named for the Taconic Mountains of

Eastern New York

Other Orogenies

• Caladonian Orogeny-Silurian event where Laurentia and Baltica collided forming a continent known as Laurasia

• Acadian Orogeny-Mid-Devonian event where Avalonia and Laurentia collided

• Antler Orogeny-Late Devonian collision of Laurentia and an Island Arc

Mid Paleozoic Life

• The Middle Paleozoic marked the first time that there was life on land

• There is evidence that plants lived on land during this time

Pangaea

• Pangaea formed during the Late Paleozoic• Pangaea was a massive supercontinent

that contained all landmasses. • The Southern portion was known as

Gondwana and consisted of South America, Africa, India and Antarctica

• Pangaea broke apart in the Early Mesozoic

Sea Level

• Pennsylvanian rocks in North America show a repeating change in sediments stacked on top of each other

• This is called a cyclothem• 50 Changes in Sea Level

Late Paleozoic Mountain Building

• Alleghanian Orogeny-Carboniferous collision between Gondwana and Laurasia.– Responsible for building the Appalachian

Mountains• Ouachita Orogeny-Carboniferous collision

between Gondwana and Laurasia

Permian Mass Extinction

• The Permian Mass Extinction marks the end of the Paleozoic.

• Also called the Permo-Triassic Extinction Event

• 95% of all species including trilobites went extinct

Permian Mass Extinction

• Affected land organisms as well• 65% of all amphibians and reptiles did not

survive

Permian Mass Extinction

• A possible cause for this was a major marine regression

• Not a lot of room for shallow marine organisms to live

• Life changed significantly at this time

Mesozoic Era

Periods Of The Mesozoic

• Triassic• Jurassic• Cretaceous • The Mesozoic runs from 250 mya-65 mya

Breakup Of Pangaea

• By the late Triassic the plates of Pangaea began to separate

• This was due to high heat beneath the surface

• Resulted in the formation of the Atlantic Ocean and the Mid Atlantic Ridge

Tectonic Activity

• Active tectonic activity in Western North America

• Formed mountain ranges known as the Cordillera

Mountain Building

• Nevadan Orogeny-Jurassic. Caused by subduction of Oceanic Plate

• Sevier Orogeny-Cretaceous. Caused an eastward shift in volcanism

• Laramide Orogeny-Cretaceous. Helped create the Rocky Mountains

• All of these occurred in Western North America

Sea Level

• Sea level dropped during the Triassic • Western North America became a lot more

arid

Sea Level

• Sea Level rose again in the Jurassic • The Appalachians began to rise as did the

Cordilleras• Massive flooding in North America• The sea covered North America from

Texas to Alaska

Mesozoic Life

• The Mesozoic is referred to as the “Age of the Reptiles”

• New marine organisms that diversified during the Mesozoic are:– Crabs– Lobsters– Shrimps– Snails

Life

• Reef builders were wiped out during the Permo-Triassic Extinction

• During the Triassic a group of clams called rudists developed the ability to build reefs in the Cretaceous

Ammonites

• Ammonites were abundant during the Mesozoic. Excellent Index Fossils

Other Life Forms

• Ichthyosaurs-Resembled Modern Dolphins• Plesiosaurs-Walrus like creatures• Mosasaurs –Sharks

Life on Land

• There was a dramatic change in life on land due to a climate shift

• Some fossils from the Paleozoic were present in Mesozoic rocks but not as prominent

• Cycads were the dominant plant

Angiosperms

• Angiosperms were another dominant plant• Angiosperms are seed bearing plants that

have flowers. First appeared in the Cretaceous

• Before the Cretaceous plants did not have flowers

Mammals

• Mammals evolved during the Triassic• Pterosuars were flying reptiles that lived

during the Mesozoic

Other Reptiles

• Crocodiles and Turtles also first appeared during the Mesozoic

• It is unknown why they survived the mass extinction at the end of the Mesozoic

Dinosaurs

• Dinosaurs were a group of reptiles that developed around 228 Million Years ago (Triassic)

• They have an upright posture while other reptiles have a sprawling posture (Their legs are not directly beneath them)

Ectothermic/Endothermic

• Ectotherms-Animals whose body temperature is regulated by the temperature of it’s surroundings. All living Reptiles are ectotherms

• Endotherms-Animals that maintain a relatively constant body temperature regardless of it’s surroundings. All living Mammals are Endotherms

Ectothermic/Endothermic

• It is controversial as to whether Dinosaurs were Ectothermic or Endothermic but there is evidence that some dinosaurs were endothermic

Mass Extinction

• Another major mass extinction occurred at the end of the Mesozoic Era.

• The following groups of organisms died:– Dinosaurs– Pterosaurs– Ammonites– Mosasaurs– Plesiosaurs

Meteorite Theory

• Geologists believe that a meteroite slammed into the Yucatan Peninsula at 240,000 kph

• Any organism that actually survived would have faced 1000 years of greenhouse warming and excessive UV radiation from the sun

-Iridium in Cretaceous Aged Rocks-Crater in the Gulf Of Mexico that also contains Iridium. Dated approximately 65 Million Years Old

Evidence

Cenozoic Era

Periods/Epochs Of The Cenozoic

• The Cenozoic is divided up as follows:– Paleogene

• Paleocene• Eocene• Oligocene

– Neogene• Miocene• Pliocene

– Quaternary• Pleistocene• Holocene

• The Cenozoic runs from 65 mya to the present

The Cenozoic

• By the beginning of the Cenozoic Pangaea had completely broken up

• The Cenozoic was a time of major climate change

Ice Age

-In the Eocene the climate started to get colder-Glaciers began to form in Antarctica

Ice Age

Ice Age

• In the Early Miocene the glaciers began to melt

• Sea level rose • However in the Late Miocene the glaciers

returned

Ice Age

• During the Pliocene the Arctic Ocean began to freeze to form an ice cap

• Late Pliocene-Pleistocene the Northern Hemisphere had extensive glaciation or an “Ice Age”

• Some glaciers were up to 3 km thick

Tectonic Events

• The Rocky Mountains were formed during the Mesozoic

• Eroded sediment filled the basin and preserved fish, insects, frogs, plants, and bird fossils

• This was known as the Green River Formation

Volcanism

• The Cascade Mountains formed at the end of the Eocene

• This was the result of the subduction of an oceanic plate beneath the western coast of North America

• During the Miocene the San Andreas Fault was formed

• Most of the volcanoes are inactive

Hot Spots

• Hot Spots are hot areas in Earth’s mantle that is stationary for long periods of time where high temperature plumes of mantel material rise towards the surface

• Yellowstone National Park is situated over a hot spot.

• The hot spot is still active

Mountain Building

• The Himalayan Orogeny occurred during the Eocene

• The Alps were formed as well• Tethys Sea

http://upload.wikimedia.org/wikipedia/commons/e/e5/Laurasia-Gondwana.png

Life

• Most of the currently living organisms evolved during the Eocene

• During the Paleocene and Eocene the Earth was predominately forests

Life

• By the late Oligocene grassy savannas supported mammals such as dogs, cats, rodents, rabbits, camels, and horses

• As the Pliocene ice age began the land became more arid

Life

• New animals came along as the Late Pliocene-Pleistocene Ice Age began:– Woolly Mammoths– Sabre-Tooth Cats

Primates

• Primates are mammals with a grasping hand and an opposable thumb

• Homo Sapiens fall under Hominids• Hominids fall under Hominoids

Hominids

• A hominid is a hominoid that:– Is Bipedal– Has a larger brain– Has smaller canine teeth– Uses sophisticated tools

Neanderthals

• Neanderthals inhabited the Earth between 200,000 and 30,000 years ago

• Neanderthals differ from humans by:– Differences in skulls– Have short, thick limbs– Have more muscular bodies– Have slightly larger brains

• We do not have a lot of information on hominids due to gaps in the fossil record