Geologic Time Chapter 21.1, 22, 23, 24

Why do we care?  By studying the characteristics of rocks and fossils within them, geologists can interpret  The environment the rocks were deposited in  Reconstruct Earth’s history  Possibly predict events or conditions of the future

Geologic Time Scale  Defn: record of Earth’s history from its origin to the present used by scientists around the world to correlate:  Geologic events  Environmental changes  Development of life-forms that are preserved in rocks  Names of periods don’t change, but the years marking the beg. and end are continually being refined.

Geologic Time Divisions  Eon – longest unit, measured in billions  Era – next-longest, hundreds of millions to billions  “Paleozoic” = old life  “Mesozoic” = middle life  “Cenozoic” = recent life  Period – 10’s to 100’s of millions of years  Epoch – smaller divisions, millions to 10’s of millions

Eons  Longest unit  Measured in billions  Three Eons  Archean Eon (part 1 Precambrian Time)  Proterozoic Eon (part 2 Precambrian Time)  Phanerozoic Eon (3 Eras)

Eras  Next-longest  Hundreds of millions to billions  Defined by differences in life-forms found in rock  Three Eras  “Paleozoic” = old life  “Mesozoic” = middle life  “Cenozoic” = recent life

Periods  Second shortest  10’s to 100’s of millions of years  Defined by life-forms that were abundant or became extinct during the time the rocks were deposited

Epochs  Smaller divisions  Millions to 10’s of millions

Precambrian Time  Makes up the first 90% of geologic time  Divided into two eons  Archean Eon (oldest)  Proterozoic Eon (more recent)  End of this eon/beg of Paleozoic Era is marked by the first appearance of organisms with hard parts (

ERAS  Landforms  Flora (plants)  Fauna (animals)  Extinctions  Climate

Paleozoic Era - Landforms - First supercontinent “Rodinia” had just broken apart - Plate tectonics, mountain building

Paleozoic Era - Flora - Rainforests covered the earth - Vascular plants appeared (allowed for taller, stronger plants) - Ferns

Paleozoic Era - Fauna - Reptiles appear - Amphibians - Fishes w/backbones (vert) - Trilobites (org w/hard parts) - Marine life!! - (Stromatolites in Precambrian)

Paleozoic Era - Extinctions - End of Paleozoic Era was the Permian Extinction (more than 90% of species died) - 1 st mass extinction ended the Ordovican period (marine life)

Paleozoic Era - Climate - Global cooling continued - Ranged from temperate to cold to steamy swamp

Mesozoic Era - Landforms - Breakup of “Pangaea” - Tectonic activity, mountain building - Sea levels rose

Mesozoic Era - Flora - Flowering plants first evolved

Mesozoic Era - Fauna - Birds evolve - Dinosaurs, Crocodiles, early mammals evolve, ocean/air reptiles evolve

Mesozoic Era - Extinctions - Cretaceous extinction ended Mesozoic era and rid dinosaurs

Mesozoic Era - Climate - Sandy, desert interior - Poles moist, temperate - Mild

Cenozoic Era - Landforms - Major tectonic activity, continents moved to their current positions

Cenozoic Era - Flora - Grasslands spread - Many more flowering plants

Cenozoic Era - Fauna - Hominids, humans, cats, whales, bats

Cenozoic Era - Extinctions - Due to changes in CO 2, we could be entering the world’s next extinction? - Just like the extinction that killed the dinosaurs?

Cenozoic Era - Climate - Most recent ice age - Climate changed back and forth, warmer and cooler