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 CO 2 into atmosphere Temps on planet warmed Mass extinction of trilobites, eurypterids, fern-like plants and many insects

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