Geologic Time

Events in Your Life

• ___When you started second grade• ___When you were born• ___ When you started kindergarten• ___When you learned to ride a bike.• ___ When you learned to walk.• ___ When you learned to read.• ___ When you lost your first tooth.• ___ Today’s date.

Construct a timeline of the important events in your life. Be sure to include all of the events listed below and any other events you feel are important. Your timeline should be constructed TWO ways:

1) Numerical Order (use actual dates)2) Sequential Order (most recent at top)

Geologic Time Scale

• Division of geologic time is based on an analysis of Earth’s rocks.

• Time units were determined by the age of fossils found in the rock layer.

• The scale that is created is called the Geologic Time Scale, it is a record of Earth’s history from its origin 4.6 billion years ago till today.

Geologic Time Division Sequence

Eon

Era

Period

Epoch

Geologic Time Divisions

• Eon is the longest time unit and is measured in billions of years.

• Examples: The Archean Eon, the Proterozoic Eon, and the Phanerozoic Eon

• The Phanerozoic Eon is the time unit we are currently in and it began 540 million years ago.

Geologic Time Divisions

• Era is the next longest span of time and is measured in hundreds of millions to billions of years.

• Era is defined by the differences in life forms found in the rock layers and is named based on the relative age of the fossils.

• Examples: Paleozoic Era, Mesozoic Era, Cenozoic Era.

Eras are subdivided into periods...periods are subdivided into epochs

Periods + Epochs = Era

• Meanings:– Zoic- “of life”– Paleo- “old”– Meso- “middle”– Ceno- “recent”

FOUR Eras…

• PRE-CAMBRIAN – 88% of earth’s history

• Paleozoic (ancient life)– 544 million years ago…lasted 300 million yrs

• Mesozoic (middle life)– 245 million years ago…lasted 180 million yrs

• Cenozoic (recent life)– 65 million years ago…continues through present day

Precambrian Era

• Atmosphere: Hydrogen and Helium probably dominant Earth’s atmosphere.– No oxygen in the atmosphere!!!!

• Plate Tectonics: Numerous volcanic eruptions released large amounts of gases into the atmosphere

Precambrian Era

• Age: – Geologist used radiometric dating to show the

Earth is at least 4.2 billion years olds• Formations:– Banded Iron Formations- alternating beds of chert

and iron oxides are now mined for iron.– Red Beds- sedimentary rocks that are younger

than 1.8 million years are rusty red in color, which shows that Earth’s was once without oxygen.

Precambrian Era

• Life: • 3.5 billion years ago the emergence of

cyanobacteria began to release oxygen in the Cambrian atmosphere.

• Nearly all Oxygen is a result of photosynthesis.• Ediacara Fauna- contained a wide variety of

organisms.

Paleozoic Era

• Plate Tectonics:– The ancient North American continent, Laurentia,

split off from Rodinia, supercontinent, and was located near the equator.

– Almost completely covered by shallow, tropical ocean.

– At the end of the Era, Pangaea formed when Laurasia( North America + Europe) collided with Gondwana (South America, Africa, India, Australia, and Antarctica)

Paleozoic Era

• Life:• Trilobites, Extinct before the dinosaurs came into existence, Cambrian Period is know as the “Age

of the Trilobites” • Articulate brachiopods were common.• Seas were dominated by corals, bryozoans, brachiopods.• Fish were dominant predator• Ferns covered the landscape during the Devonian.• Amniotes egg evolved and allowed reptiles to colonize dry

land.

Early Fish

Early fish did not have jaws.

Some species of sharks were in existence at this time.

Early Land Plants

Cone bearing plants

Ferns

Mosses

Paleozoic Era

• Two major mass extinctions:– Ordovician Period- 75% of all marine genera became

extinct, • Caused by an episode of global cooling, glaciations.

– Permian Mass Extinction- larges mass extinction in the history of life.• Permo-Triasic Extinction Event -95% of all species including

trilobites were impacted.• Possible reason

– Lowering of sea levels when the continents were rejoined as Pangaea (convergent boundary)

– Increased volcanic activity (ash and dust)– Climate changes – cooler climate

Mesozoic Era

• Plate Tectonics:– Pangaea broke apart

• Life:– Modern marine fauna present.

• Ex. Crabs, lobsters, shrimps, sponges, modern corals, snails, bony fish, sharks, aquatic reptiles, and aquatic mammals.

– Dinosaurs dominated the land.• Gymnosperms or plants that produce seeds, but no

flowers. – Pine Trees

• Flowering plants appeared during the END of this era.

Dinosaurs

Mesozoic Mammals

Mesozoic Era

• This era ended with a mass extinction event about 65 million years ago.– Many groups of animals, including the dinosaurs

disappeared suddenly at this time.

• Many scientists believe that this event was caused by a comet or asteroid colliding with the Earth.

Mesozoic Era – Mass Extinction Event

• Asteroid or Comet collides with Earth.

– Huge cloud of smoke and dust fills the air– Blocks out sunlight– Plants die– Animals that eat plants die– Animals that eat plant-eaters die.

• However, not all forms of life died during this event. Many animals that you see today are descendants from the survivors of this extinction event.

Cenozoic Era• Age:

– Began about 65 million years ago and continues today!!!!!• Climate was warm and mild.• Marine animals such as whales and dolphins evolved.

• Plate Tectonics:– Many mountain ranges formed during the Cenozoic Era

• Alps in Europe and Himalayas in India; Rocky Mountains in the USA

– Glaciers extended as far south as Ohio and Missouri Rivers. • Life:

– This era is sometimes called the “Age of Mammals”– Large mammals and Primates, dogs, cats, etc.– Homo Sapiens- Humans

Cenozoic Mammals

Flowering Plants were common during the Cenozoic Era

Geologic Time Divisions

• Periods are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited.

• Usually measured in tens of millions of years to hundred of million of years.

• They are named for the geographic region were the rocks were first observed.– Example: Mississippian Period and Jurassic Period

Geologic Time Divisions

• Epochs are the smallest unit of geologic time and are usually measured in millions of years to tens of millions of years.

• Epoch’s are based off specific groups of organisms that have been distinguished.– Example: Oligocene Epoch is based off the marine

fossils, and the Eocene Epoch is based on terrestrial plants

Video

• Life after Dinosaurs:• https://www.youtube.com/watch?v=b7QSwA

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