1. Geologic Time Scale
Earth Science Spring 2014

2. The Geologic Column
Geologic column- arrangement of rock layers based on the ages of the rocks
No single area on earth a record of all geologic time
Observations from around the world were used to create the geologic column
Represents a timeline of the earth’s history
Rock layers are distinguished from one another primarily by the fossils they contain and the type of rock they are made of
Using the law of superposition and the study of fossils, nineteenth century scientists determined the relative ages of rock layers in areas throughout the year.
Fossils in the upper more recent layers are resemble more modern plants and animals. Most of the fossils in. the. Lower older layers are from species that have been long extinct.

3. Divisions of Geologic Time
Earth’s history is divided by:
Major surface or climate changes
Extinction of various species
**these types of events are used to divide the geologic time scale into smaller units
Just like the calendar is broken into years, months, weeks, days & geologic time is divided into units. \
The geologic history of the earth is punctuated by major changes in the earth’s surface or climate and by the extinction of various species
Rocks grouped within each unit contain a similar fossil record …a unit of geologic time is often characterized by fossils of a dominant life form
The geologic history of the earth is punctuated by major changes in the earths surface or climate and by the extinction of various species.

4. Divisions of Geologic Time
Eras
Era- largest unit of geologic time
4 geologic eras
Precambrian
Paleozoic
Mesozoic
Cenozoic

5. Divisions of Geologic Time
Eras
Precambrian Era (Precambrian Time)
Earliest era
Oldest layer of the geologic column
Longest era (4 billion years)
Very few fossils
Makes it difficult to divide into smaller units
Bacteria, algae, primitive worms, sponges, & corals
Evidence that life started in the ocean
Much longer than the other three geologic eras
Very few fossils exist from this time so it is very difficult to divide the 4 billion years of the precambrian era into smaller units.
Very early rocks of this era contain no life, but there are a few fossils of bacteria & algae

6. Divisions of Geologic Time
Eras
Paleozoic Era
2nd era
Means “ancient life”
292 million years long
Fossils- wide variety of both marine & land plants & animals

7. Divisions of Geologic Time
Eras
Mesozoic Era
3rd era
Means “Middle Life”
183 million years long
Fossils- more complex organisms like reptiles & birds

8. Divisions of Geologic Time
Eras
Cenozoic Era
Present geologic era
Means “recent life”
Fossil- mammals are common
The fossil sequence in the geologic column show that earlier forms of life generally were followed by new and more complex forms,

9. Divisions of Geologic Time
Periods- subdivision of a geologic era
Characterized by specific fossils
Named for the location in which the fossils were first found
Epochs – subdivision of a geologic time period
Contain an extremely detailed fossil record
2 period of the cenozoic era are divided into these

10. Geologic History Theory of evolution
Theory that organisms change over time and that new organisms are derived from ancestral types.
First proposed by Charles Darwin by way of natural selection (survival of the fittest)
Evidence:
Fossil record
Examination of living organisms
The geologic history of the earth is recorded in rock layers. The type of rock that makes up each layer and the fossils that are found in each layer reveal lots about the conditions that existed when the layer formed. For example, limestone forms in bodies of water. The presence of a limestone layer in a region indicates that the area was once covered by water. Cross-bedded sandstone often forms from sand dunes. The presence of this sandstone may indicate that desert or coastal dune area existed at one time.
Natural selection: organisms are adapted to their environment because of this adaptation changes in the environment affect the organisms living in it. Only those organism that can adapt survive, organisms that do not adapt will become extinct.

11. Geologic History Theory of Evolution cont…
Geologic changes & climatic changes affect the survival of organisms
Example of geologic change is a dramatic decrease in the amount of the earth’s surface covered by water
Example climatic change is a decrease in atmospheric temperature
Water: at one time vast areas of the surface of the earth were covered by warm shallow waters, these waters have receded .
Climate: decrease in atmospheric temperature, this occurred during the time of ice ages that have affected the earth at various times

12. Geologic History Precambrian Time Makes up 88% of the earth’s history
Began with the formation of the earth 4.6 billion years ago & ended 540 million years ago
Rocks from this era are difficult to interpret
Shields of precambrian rock are found on every continent
Fossils are rare
Most common are stromatolites
The precambrian rock record is difficult to interpret because most precambrian rocks have been severely deformed & altered by crustal activity that the original order of rock layers is rarely identifiable.
Shields: result of several hundred million years of volcanic activity, mountain building, sediment formation, and matamorphism. Nearly half the valuable minerals in the world have been found in rocks of Precambrian Shields.
Fossils: rare in precambrian rocks probably because Precambrian life forms were soft bodied. These organism lacked bones or shelss, or other hard parts commonly found in fossils. These rocks are also extremely old so folding, faulting, and volcanic activity have probably destroyed most precambrian fossils over time
Stromatolites--- reeflike deposits produced by cyan bacteria. They still form today in warm shallow waters. The presence of these indicates that shallow seas may have covered much of the earth during some periods of the precambrian era. Other fossils found include imprints of jellyfish, marine worms, & other single celled organisms and were first found in the rocks of Australia but have since been found on the other continents.

13. Stromatolites

14. Geologic History Paleozoic Era
Began 540 million years ago & ended about 248 million years ago
It is believed that Pangea formed by the end of this era
Abundant fossil record
Rich in marine & land animal & plant fossils
Divided into 7 periods
Scienctists theorize that at the beginning of this era the earth’s landmasses were scattered in a large world ocean but by the end the landmasses had collided to form one big super continent pangea. The tectonic activity that was created by this made new mountain ranges & lifted large areas of land above sea level.
Fossils from this era suggest a dramatic increase in both plant and animal life. Because of all of the fossils they have divided the paleozoic era into 7 periods. We will talk about each period individually.

15. Geologic History Paleozoic Era- Cambrian Period
Contains the first advanced marine life
Most of the continents were covered with warm, shallow oceans.
Marine invertebrates thrived here
Invertebrates- animals without backbones
Most common- trilobites
Brachiopods- shelled animals
2nd most common type of animal to live during this time
Still no evidence of land-dwelling plants or animals
Marine organisms displaced the primitive precambrian organisms as the dominant form of life. The explosion of marine life may have been due to the warm, shallow seas that appear to have coverd most of the continents during this period.
Trilobites- hard shelled animals that lived on the ocean floor. Scientists use trilobites as an important index fossil for identifying layers of Cambrian rock throughout the world
Brachiopods- shelled animals, there is evidence that there were at least 15 different families of brachiopods during this period. There are still a few kinds of brachiopods that exist today.
Other common Cambrian invertebrates include worms, jelly fish, snails, and sponges. No evidence of land-dwelling plants or animals has been found among any of the Cambrian fossils discovered so far.

16. Geologic History
Cambrian Period

17. Geologic History Paleozoic Era- Ordovician Period
Number brachiopod species increased & number of trilobites decreased
Large number of coral started to appear
Graptolite- useful index fossil
First vertebrate appeared
Vertebrate- animal with a backbone
Still no plant life on land
During the Ordovician Period, the number of brachiopod species increased & the number or trilobites decreased. Snails, clams, & other mollusks became the dominant life-forms. Large numbers of coral began to appear & colonies of graptolites flourished in the oceans. Graptolites are useful index fossils for this period.
An important development of this period was the appearance of the ostracoderm, a primitive fish,. Fossils of ostrocoderms are the oldest fossils of vertebrates. Had no jaw or teeth & their bodies were covered with bony plates.

18. Geologic History
Ordovician Period

19. Geologic History Paleozoic Era- Silurian Period
Marine life continued to thrive & evolve during this time.
Echinoderms became more numerous
Eurypterids- scorpion-like sea creatures were abundant
Near the end, land plants & animals started showing up
Ex: spiders, millipedes
Marine life, both invertebrate & vertebrate, continued to thrive & evolve. Echinoderms, relative of modern sea stars, and corals became more numerous. Scorpion-like creatures called eurypterids were abundant during this period. Fossils of giant eurypterids about 2.7 meters in length have been found in western New York.
Near the end of this period the earliest plants and animals were found on land…lik spiders & millipedes evolved on land.

20. Geologic History
Silurian Period

21. Geologic History Paleozoic Era- Devonian Period
Many kinds of bony fish
Lungfish- air breathing fish
Rhipidistians- land going fish
1st true amphibian showed up
Ichthyostega- like a huge salamander
Land plants began to develop
Giant horsetails, ferns, cone-bearing plants.
Often called the age of fishes because rocks from this period contain fossils of many kinds of bony fishes. One type of fish, the lung fish had the ability to breath air. Other air-breathing fish called rhipidistians, had strong fins that probably enabled them to crawl out of the water for a short periods of time.
The first true amphibian, probably eveolved from these fish. Resembled a huge salamandar, is though to be an ancestor of modern amphibians like frogs and toads.
During this period, land plants, such as giant horsetails, ferns, and cone-bearing plants, began to develop

22. Geologic History
Devonian Period

23. Geologic History
Paleozoic Era- Carboniferous Period (Pennsylvanian & Mississippian)
Climate was generally warm & the humidity was high all over the world
Forests & swamps covered much of the land
Amphibians & fish continued to thrive
Crinoids were common in oceans
Insects were common on land
Reptiles appeared & resembled large lizards
Many of the coal, oil, & natural gas deposits are found in rocks from this period
In North America, the Carboniferous Period is divided into the Mississippian & Pennsylvanian Periods. During this time the climate was generally warm & very humid all over the world.
Much of the landmasses were covered in swamps and forests.
Amphibians & fish continued to fluorish during this period.
Crinoids, relative of modern sea starts, were common in the oceans.
Insects such as giant cockroaches and dragonflies were common on land.
Toward the end of the Pennsylvanian Period, repites, the first vertebrates fully adapted to life on land, appears. These early reptiles resembled large lizards.

24. Geologic History
Carboniferous Period

25. Geologic History Paleozoic Era- Permian Period
End of the Paleozoic Era
Mass extinction of many Paleozoic life forms
Nearly all continents had joined to form Pangea
Areas of desert & savannah formed in the interior of the continent
Shallow seas evaporated
Many species of marine invertebrates became extinct
The permian period marks the end of the Paleozoic Era & a mass extinction of numerous Paleozoic life-forms. Neraly all the continents of the world had joined to form Pangaea.
Collision of tectonic plates forced the appalachian mountains to rise so high the moist air could not rise over the mountain tops, areas of desert & dry savanna climates developed.
The shallow inland seas evaporated. As the seas retreated, many speices of marine invertebrates including trilobites & eurypterids became extinct. Fossils indicate that reptiles & amphibians were able to survive the changes in climate.
In the following geologic era, the Mesozoic, reptiles would dominate the earth.

26. Geologic History Mesozoic Era Began 248 million years ago
Ended 65 million years ago
Pangea broke up into the continents
Tectonic plates drifted & collided forming mountain ranges
Shallow seas & marshes covered most of the land
Climate was warm & humid.
Favored reptiles
Geologic evidence show that during this era the surface of the earth changed dramatically. Pangaea began to break up into separate continents.
The tectonic plates drifted & collided, uplifting mountain ranges such as the Sierra Nevadas & the Andes in South America.
Shallow seas and marshes covered much of the land masses. The continental climates were generally warm and humid.
Conditions during this era favored the survival of reptiles. Lizards, turtles, crocodiles, snakes, and dinosaurs fluorished.

27. Geologic History Mesozoic Era- Triassic Period
Dinosaurs first appeared
Dinosaurs varied greatly in size
Lush forests of cone-bearing trees & cycads
New forms of marine life appear
Earliest mammals made their appearance
The word dinosaur comes from the Greek words meaning terrible lizard.
Dinosaurs varied greatly in size. Some were no larger than squirrels and others weighed as much as ten elephants and were nearly 30 meters long.
Most of the dinosaurs during the Triassic Period were only about 4-5 meters in length and moved very quickly.
Cycads are plants that were similar to today’s palm trees.
Reptiles called ichthyosaurs inhabited the earth during this time.
Most common marine life was the ammonite, a type of shellfish similar to the modern nautilus. The fossils of these are an index fossil for the mesozoic era.
The very earliest mammals made their appearance, small rodent life forest dwellers.

28. Geologic History Mesozoic Era- Jurassic Period
Dinosaurs were the dominant form of life
2 major groups of dinosaurs evolved.
Saurischians- both carnivores & herbivores
Ornithischians- herbivores
Flying reptiles were common
Dinosaurs became the dominant form of life. Fossil records indicate that 2 major groups of dinosaurs evolved. These dinosaurs are distinguished by their hip-bone structures. One group was calle saurischians (lizard hipped) included herbivores (plant eaters) & carnivores (meat eaters). The other major group was the ornithischians (bird hipped) were herbivores. Stegosaurus is one of these.
Flying reptiles were also common. They had skin covered wings much like today’s bats
Also found in the fossil record from this period was one of the first birds with feathers.

29. Geologic History Mesozoic Era- Cretaceous Period
Dinosaurs continued to dominate the earth
Tyrannosaurus rex
Ankylosaurs-armored bodies
Ceratopsians- horned
Ornithopods- duck-billed
1st flowering plants appeared (angiosperms)
End of this period was marked by a mass extinction
Dinosaurs continued to dominate the earth during the Cretaceous period.
T-rex had huge jaw with razor sharp teeth.
Ankylosaurs- bodies covered in bony armorlike plates
Ceratopsians, Ornithopods, & Ankylosaurs are all herbivores.
Plants- most of the angiosperms that appeared were willows and magnolias
Later on trees like maples, oaks, and walnuts became abundant. These types of plants were so successful that they still are the dominant land plants of today.
The end of the Cretaceous period was marked by the mass extinction of many species, including all dinosaurs and marine animals. No dinosaur fossils have been found in rocks after the cretaceous period.
2 possibilities are a meteorite impact hypothesis or possibly a drastic climate change due to the movement of continents and increased volcanic activity.

30. Geologic History Cenozoic Era (Age of the Mammals)
Began 65 million years ago
Continents in the beginning looked much like they do today
Increased tectonic activity
Dramatic climate changes
Mammals became the dominant life form
Continents shapes were much like they appear today but they were much closer together.
As crustal plates collided, huge mountain ranges were formed (Alps, Himalayas)
Dramatic climate changes appear to have occurred. At times, continental ice sheets covered nearly a third of the earth’s land areas. As temperatures fell during the ice ages, various species became extinct and other species appeared.
Mammals became the dominant life form and underwent tremendous evolutionary change.

31. Geologic History Cenozoic Era (Age of the Mammals) 2 periods Tertiary
Time before the last ice age
Quaternary
Began with the last ice age & includes present time
** divided into 7 epochs
Tertiary- Paleocene, Eocene, Oligocene, Miocene, & Pliocene
Quaternary- Pleistocene & Holocene

32. Geologic History
Cenozoic Era: Paleocene & Eocene Epochs (Tertiary Period)
Paleocene Epoch
Many new mammals evolved
Small rodents
1st primates appeared
Eocene Epoch
First flying squirrels, bats, and whales appeared
Smaller reptiles flourished
World wide temperature dropped 4 degreed Celsius
The fossil record indicates that during the paleoene epoch many new mammals evolved. There were small rodents, about the size of modern squirrels or mice, and a few small carnivores. Fossils of the first primates, called lemuroids are found here. Lemuroids were small, tree dwelling mammals with thick fur and long tails.
Other mammals, including the hyracotherium, which is the earliest ancestor of the horse developed during this period. Fossil records indicate that the first flying squirrels, bats, and whales appeared during this epoch. Although the dinosaurs had become extinct, smaller reptiles continued to fluorish. Worldwide temperatures dropped 4 degrees celsius during this epoch.

33. Geologic History
Cenozoic Era: Oligocene & Miocene Epochs (Tertiary Period)
Oligocene Epoch
Climate continued to become cooler & drier
Early mammals became extinct
Larger species of today’s common animals flourished
Himalaya mountains formed
Miocene Epoch
Climate still dry & cool
Golden Age of Mammals
Common fossils include: deer, rhinoceros, & pig families
Largest known mammals lived
Modern polar ice caps started to form
Geologic evidence indicates that during the Oligocene Epoch, the climate continued to become cooler and drier. This favored the growth of grasses and cone-bearing and hardwood trees.
Many of the earlier types of mammals became extinct, however, larger species of deer, pigs, horses, camels, cats, and dogs fluorished .
Indian subcontinent continued to collide with the Eurasian continent, uplifting the Himalayas.
The climate remains cool and dry. Large herds of primitive horses and camels roamed the plains.
Fossils remains of members of the deer, rhinoceros, & pig families are found in rocks from this time. Also there are fossils from raccoons, wolves, foxes, and the saber tooth cat.
Circumpolar currents were established around antarctica and the modern polar ice caps began to form.
Tectonic forces and dropping sea levels caused the Mediterranean Sea to dry up and refill several times.

34. Geologic History Cenozoic Era: Pliocene Epoch (Tertiary Period)
Hunting animals became fully evolved
Fossils of first modern horses
Great climatic changes occurred & continental ice sheets began to spread
Land bridge between Eurasia & North America appeared
North & South America became connected by the central American Land Bridge
During the pliocene epoch, hunting animals- members of the bear, dog, and cat families became fully evolved. These animals hunted herds of grazing animals that inhabited the plains. Fossil of the first modern horses have now been found.
Before the end of the Pliocene Epoch, great climatic changes occurred, and the continental ice sheets began to spread. With so much water locked up in ice the Bering land bridge between Eurasia & North America appeared as sea level dropped.
The uplifting of crust between north and south america caused the central American land bridge.
The formation of theses two land bridges allowed many species to migrate between the continents.

35. Geologic History
Cenozoic Era: Pleistocene & Holocene Epochs (Quaternary Period)
Pleistocene Epoch
Several periods of glaciation occurred over most of North America & Eurasia
Many animals became extinct
Fossils of early ancestors of humans
Holocene Epoch
Began about 11,000 years ago as the last ice age ended
Sea level rose drastically as glaciers & ice sheets melted
Great Lakes were formed
Modern humans developed
Agriculture developed
Use of bronze & iron tools began
Some animals had special characteristics that allowed them to endure the glaciation, like the thick fur covered wooly mammoth and rhinoceroses, other animals moved to warmer climates.
Fossils of early ancestors of humans are found in this epoch. Scientists have evidence that indicates early humans were hunters. Their successful hunting may have been one factor that led to the extinction of many large mammals during this epoch.
As large ice sheets melted, sea level rose an estimated 140 meters & coastlines took on their present shapes.
Compared with the entire geologic time scale, human history is extremely brief. If you think of the entire history of the earth as one year, the first organisms would have appeared early in May. Early humans would have appeared on December 31st at 7pm; and modern humans not until 11:55 pm that night.