GEOLOGIC TIME

ESRT PAGES 8 and 9

AGE OF EARTH

• 4.6 Billion Years old = 4600 Million Years old

• MYA = millions of years ago

GEOLOGIC TIME

• Based on fossil evidence and mass extinctions

• Life forms have evolved over time

• 4 MAJOR ERAS

1. PRECAMBRIAN

• Longest era 4.6 billion years to 544 million years ago,

longest geologic era, lasted about 4 billion years • No fossil record – WHY?

a. Most rocks were non-sedimentary because the earth was still cooling

b. Small organisms with no hard shells

Ending of Precambrian Era sees a sudden explosion of life due to evolution of atmosphere

What process added oxygen to the atmosphere?

photosynthesis

2. PALEOZOIC

• 544 million years to 251 million years ago

• Invertebrates

• Fish, amphibians, vertebrates

• land plants first appear

At the end of Paleozoic

• massive climate change and mega volcanoes that erupted for centuries

• Massive release of CO2 into atmosphere

• Temps on planet warmed

• Mass extinction of trilobites, eurypterids, fern-like plants and many insects

http://en.wikipedia.org/wiki/Image:Haeckel_Eurypterid.jpg

3. MESOZOIC

• 251 million years to 65 million years ago

• Dinosaurs

• Earliest Birds and mammal

• Extinction of dinosaurs

• 63 Millions years ago

At end of Mesozoic

• Asteroid impact

• Vast cloud of searing vapor and debris raced over continents incinerating everything in its path

• Pulverized rock was ejected

• Enough heat was generated to broil surface of planet

• Lots of sulfur in the air

• All dinosaurs became extinct as well as many, many other organisms

• Evidence of impact crater is in the Yucatan peninsula in Mexico

4. CENOZOIC

• 65 million years ago to present

• Modern plants and animals

• Last 2 million years - age of man,

dominated by glaciation