A View of Earth’s Past

Earth and Space ScienceAustin High School

2015-2016

Geological Time Earth’s surface is constantly changing

As conditions change, organisms flourish an than later become extinct

Evidence of change is recorded in the rock layers of earth’s crust

To describe the sequence and length of change, scientist have developed a geologic time scale

The scale outlines the development of earth ad life on earth

The Geological ColumnApplying the principle that old layers of rock are below young

layers scientist determine the relative ages of sedimentary rock in different areas around the world

No single area on earth contain a record of all geologic time, scientist combined their observations to create a standard arrangement of rock layers

The Geological ColumnOrdered arrangement of rock layers is called a geologic

column

Geologic column represent a timeline of the earth’s history

Oldest rock at the bottom of the column

Columns are distinguished by the rock type and kinds of fossils the layers contain

Fossils in upper layers layers resemble modern plants/animals, where lower (older) layers fossils differ from those living today

The fossils discovered in old layers are from species that have been extinct for millions of years.

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Using a Geologic ColumnGeological columns were first developed using factors such

as average rates of sediment deposition to estimate the age of rock layers

Development of radiometric dating (ex. Carbon dating) to determine the absolute ages of rock layers with more accuracy

Geologic columns can now be used to estimate the age of rock that cannot be dated radiometrically

A comparison between a given rock layer and a similar layer in a geologic column (contains same fossils or same relative position) can be used to determine age

Division of Geologic TimeGeological history of earth is marked by major change in

earth’s surface, climate, and types of organisms

Geologist use these indicators to divided the geologic time scale into smaller units

Geological time is generally characterized by fossils of a dominant life-form.

Scientist commonly use abbreviations when they discuss geologic time (so long) Ma = mega annum, which means “one million years”

Eons and ErasLargest unit of geologic time is an eon

Geologic time is divided into four eonsThe Hadean eonThe Archean eonThe Proterozoic EonThe Phanerozoic Eon

The first three eons are part of a time internal commonly known as Precambrian time

Precambrian is a 4 billion year interval that contains most of earth’s history

Very few fossils exist in early Precambrian rocks, so dividing Precambrian time into smaller time units is difficult

Precambrian

Eons and ErasAfter Precambrian time the Phanerozoic eon began

This eon is divided into smaller units of geologic time called eras

The first era of the Phanerozic eon was the Paleozoic Era which lasted 291 millions years

Paleozoic rocks contain fossils of wide variety of marine and terrestrial life forms

The Mesozoic Era Began after and lasted 186 million years

Mesozoic fossils include early forms of birds and reptiles

The present geologic era is the Cenozoic Era which began 65 million years ago.

Fossils of mammals are common in Cenozoic Rocks

Period and EpochsEras are divided into shorter time units called periods

Each period is characterized by specific fossils and are usually named for the location in which the fossils were first discovered

Where rock records are most complete and least deformed, ad detailed fossils record may allow scientist to divide periods into shorter time units called epochs

Epoch may be divided into smaller units of time called ages which are defined by the occurrence of distinct fossils in the fossil records

EvolutionFossils indicate the kinds of organisms that lived when rock

formed

By examining rock layers and fossils scientist have discovered evidence that species of living things have changed overtime, process called evolution

Evolution is the gradual development of new organisms from preexisting organisms

Evidence for evolution includes the similarity in skeletal structures of animals

Theory of evolution by natural selection was proposed by 1859 by Charles Darwin

Evolution and Geologic ChangeGeologic and climate change can affect the ability of some

organisms to survive

Using geologic evidence, scientists try to determine how environmental changes affected organisms in the past

Fossils records show that some organisms survived environmental changes while other organisms disappeared

Fossils are used to learn why some organisms survived long periods of time without changing while other organisms changed or became extinct

Precambrian Time

Precambrian TimeEarth was formed about 4.6 billion ears ago as a large cloud or

nebula spun around the newly formed sun

Material spun around the sun, particles of matter began to clump together and eventually formed earth and the other planets of the solar systems

The time interval that began with the formation of Earth and ended about 542 million years ago called known as Precambrian time.

This division of geologic time makes up about 88% of Earth’s history

Relatively little is known about what happened during this time

Information is lacking because rock record is difficult to interpret

Precambrian are so severely deformed and altered by tectonic activity that the original order of the rock layer is rarely identifiable

Precambrian RocksLarge areas of exposed Precambrian rocks, called shields

exist on every continent

Shields are a result of several hundred millions years of volcanic activity, mountain building, sedimentation, and metamorphism

Precambrian shield were lifted and exposed at earth’s surface

Half of the valuable minerals deposits in the world occur in rocks of Precambrian shields

Valuable minerals include nickel, iron, gold, and copper

Precambrian LifeFossils are rare in Precambrian rocks because life-forms lack

bones, shells, or other hard parts that commonly form fossils

Precambrian rocks are old, nearly 3.9 billion years

Volcanic activity, erosion, and extensive crustal movements probably destroyed most of the fossils that may have formed

The most common Precambrian fossil are Stromatolites

Stromatolites are reef like deposits formed by blue-green algae

Stromatolites indicate tha shallow seas covered much of Earth during periods in Precambrian time

Imprints of worms, jellyfish, and single-celled organisms have also been discovered from late Precambrian time

The Paleozoic Era• Cambrian Period• Ordovician Period• Silurian Period• Devonian Period• Carboniferous Period• Permian Period

The Paleozoic EraGeological Era that began 542 million years ago and ended

about 251 million years ago

At the beginning of this era, Earth’s landmasses were scattered around the world

By the end, landmasses had collided to form the super-continent Pangaea

Tectonic activity created new mountain ranges and lifted large area of land above sea level

Paleozoic rocks hold an abundant fossils records

# of plant and animal species on earth increased dramatically at the beginning of this Era

The Cambrain PeriodVariety of marine life-form appeared during this periods

life-forms were more advanced than previous life-forms and quickly displaced the primitive organisms as the dominant life-forms

Marine invertebrates, animals that do not have backbones, thrived in the warm waters

Most common invertebrates were trilobites

2nd most common animal, brachiopods, a group of shelled animals

Other common Cambrian invertebrates included worms, jellyfish, snails, and sponges

No evidence of land-dwelling plants or animals discovered

The Ordovician PeriodDuring this period trilobites began to shrink

Clamlike, Brachiopods and cephalopods became dominant invertebrates life-forms

Large # of corals appeared

Vertebrates, animals that have backbones, had appeared

Most primitive vertebrates were fish

Ordovician fish did not have jaw or teeth and their bodies were covered with thick, bony plates

No plant life on land

The Silurian PeriodVertebrate and invertebrate marine life continued to thrive

Echinoderm (relatives to modern sea stars) and corals became more common

Eurypterids, Scorpion-like sea creatures existed during this period

Fossils of giant of these creatures nearly 3 meters long were discovered in western New York

Near the end of period, earliest plant and animals evolved on land

The Devonian PeriodCalled the Age of Fishes

Many fossils of bony fishes were discovered in rocks

Lungfish, were fish that has the ability to breathe air

Fist amphibians evolved, resembled huge salamanders

During this periods, land plants began to develop

In the sea, brachiopods and mollusk continued to thrive

The Carboniferous PeriodClimate was generally warm and high humidity

Forest and swamps covered much land

Amphibians and fish continued to flourish

Insects, giant cockroaches and dragonflies were common

This period is divided into two periods: Mississippian and Pennsylvanian

Vertebrates that were adapted to life on land appeared, these early reptiles resembled large lizards

The Permian PeriodPermian period marks end of Paleozoic Era

A mass extinction of large number of Paleozoic life-forms occurred

Collision of tectonic plates created the Appalachian Mountains

Shallow inland seas that had covered much of earth disappeared

As sea retreated, many species of marine invertebrates became extinct

Reptiles and amphibians survived the environmental changes and dominated Earth in the million years that followed

End of Permian, 90% of marine organism and more than 70% of land organisms died

Mesozoic Era

The Mesozoic Era Geological era began about 251 million years ago and ended

about 65 million years ago

Earth’s surface changed dramatically, Pangaea broke into smaller continents and tectonic plated drifted and collided

Collision uplifted mountain ranges such as the Sierra Nevada in California and Andes in South America

Shallow seas and marshes covered much of the land

Climate was warm and humid

Lizards, turtles, crocodiles, snakes, and variety of dinosaurs flourished

Also known as the “Age of Reptiles”

This Era has rich fossil records and is divided into three periods

The Triassic PeriodDinosaurs appeared during this period

Some dinosaurs were the size of squirrels and some weighed as much as 15 tons

Forest were lush with cone-bearing trees and cycads which are plants that resemble the palm trees of today

Reptiles called ichthyosaurs lived in the Triassic oceans

During this time the first mammals, small rodent-like forest dwellers appeared

The Jurassic PeriodDinosaurs became the dominant life-form

Fossils indicate two major groups of dinosaurs evolvedSaurischians = “lizard-hipped”

Included herbivores (plant eaters) and carnivores (meat eaters)Ornithischians = “bird-hipped”

Flying reptiles called pterosaurs were common during this period

The Cretaceous PeriodDinosaurs continued to dominate

Tyrannosaurus rex existed during this time

Other dinsosaur included ankylosaurs, ceratopsians, hadrossaurs

Plant life become very sophisticated

Earliest flowering plants or angiosperms appeared

Most common of these plants included trees (magnolias and willows),

Dinosaurs became extinct

The Cenozoic Era

The Cenozoic EraDivision of time that began 65 million years ago and

includes the present time

Continents moved to their present-day positions

Plated collided to form Alps and Himalayas Mountain ranges

Dramatic change in climate occurred

Mammals became the dominant life-form and underwent many changes

“Age of the Mammals”

Cenozoic EraDivided into 2 periods:

Tertiary period - First primates appear and flowering plants become the most common.

Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.

The End