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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 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