Earth History: Geologic Time

Geologic Time• Geologic Time: It is very, very long.

– Earth is estimated to be around 4.6 billion years old based on the rock and fossil record.

– Geologic time is broken up into sections based on major changes in Earth .

Divisions of Geologic TimeLargest Division: Eons

–Eons divided into Eras: –PreCambrian, Paleozoic, Mesozoic,

Cenozoic»Ceno - recent»Meso - middle»Paleo - ancient»Zoic - life

»Eras are divided into Periods

PreCambrian543 million years ago to ~ 4 billion years ago (?)

–“Age of Bacteria”• Oldest Era• Longest era because we know so little

about the earth that long ago• Life: Very little life: only basic forms

including bacteria, the oldest fossils ever found, seaweed, jellyfish, and worms– Photosynthesis of the seaweed added

oxygen to the early atmosphere, paving the way for land life.

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First Life One celled plants

(algae) entered the fossil record approximately 3 b.y. ago (Precambrian).

Large colonies of this algae are called stromatolitesstromatolites.

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More Atmospheric Changes

Through photosynthesis, O2 was released

into the atmosphere and ocean allowing animals to eventually evolve.

Paleozoic543 million years ago to 248 million years ago

• “Age of the Fish”• Explosion of life in the sea: trilobites,

shellfish, Fish• Life appears on land: Ferns, Amphibians

• Pangaea formed• Largest mass extinction ever at the end

of the Paleozoic. 90% of species became extinct.

Paleozoic Organisms

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Carboniferous Time In Europe the

Mississippian and Pennsylvanian periods are together called the

Carboniferous

period. Vast swamps and forests from that time created the huge

coal beds found throughout eastern United States.

Mesozoic248 mya- 65mya

• “Age of the Reptiles”• Life: Reptiles are the dominant life on land.

Dinosaurs exist. Birds appear. Forests of trees appear

• Pangea broke apart during this peroid.

• Dinosaurs become extinct in a mass extinction at the end of the Mesozoic.

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Reptiles: Appeared in the Permian and quickly

became the dominant life form.

…until Dinosaurs took over.

They ruled the planet throughout the Mesozoic era (the “Age of Dinosaurs”).

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Birds

Some of the dinosaurs are thought to have evolved into birds.

Archaeopteryx is the oldest fossil bird found to date.

Dinosaur Extinction1. Volcanoes

erupt and fill the atmosphere with CO2 and gasses that BLOCK the sun light preventing plant life…….

2. Meteorite

impact causes multiple natural disasters

Evidence of a Meteorite

• Layer of Iridium in rock layers

Cenozoic65 mya- present

• “Age of the Mammals”• Life: Large mammals appear, Humans

appear

• Ice Ages occur and ice sheets advance

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Mammals

Mammals first appeared in the Mesozoic as small rodents. After the dinosaurs were erased at the end of the Mesozoic, Mammals quickly evolved to become the dominant life form.

The Cenozoic is the “Age of Mammals”.

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Present

We live in the Holocene epoch, of the Quaternary period, of the Cenozoic era.