Scientists have divided geologic history into 4 main parts: Precambrian Time Paleozoic Era Mesozoic Era Cenozoic Era

 4.6 billion – 543 million years ago  Life began during this time  Atmosphere made of water vapor, CO 2 & N 2  Volcanic eruptions, meteorites, violent storms & intense solar radiation

Extraterrestrial Life came from outside the planet(i.e. meteor) Creation Divine forces created life Non-Living Matter Spontaneous assembly of molecules

4 billion years ago - Earth began to cool Water condensed and fell as rain

Atmosphere of early Earth  Hydrogen (H 2 )  Volcanic gas (i.e. methane (CH 4 ), ammonia (NH 3 ), CO, SO 2, N 2, CO 2 )  No free oxygen or ozone

 Energy stimulated chemical reactions = Proteins Nucleic Acids LipidsCarbohydrates UV +

 In the oceans  Energy from radiation and storms caused simple chemicals in the oceans & atmosphere to react  More complex molecules were made  Molecules joined to form cells  Prokaryotes: single-celled organisms (without a nucleus) that did not need O 2 to survive

 Cyanobacteria (type of prokaryotic organism) appears over 3 bya  Uses sunlight to produce food

 Oxygen gas is released into oceans & air  Oxygen molecules react to form Ozone, which absorbs harmful radiation form the sun  Now possible for life to exist on Earth’s surface

 VOCs  Volatile organic compounds  NOx  Nitrogen-oxygen compounds

 Eukaryotes appear in the fossil record  Organism that contain a nucleus  Will evolve into organisms composed of many cells

 “Old life” or “Ancient life”  Large fossil record  Sponges, coral, squid, clams, trilobites, fish, sharks  Reptiles, amphibians, fish, worms, & ferns first appear

 Plants, fungi, & air-breathing animals slowly colonized land  Crawling insects first animals to live on land  Reptiles & winged insects appear near the end of era  LARGEST Mass extinction marks end of era  90% of species extinct  Oceans completely changed

 “Middle Life” or “Age of Reptiles”  Dinosaurs dominate Earth for 150 million yrs  First birds appear  Conifers appear  Flowering plants appear late in era

 Mass Extinction  Dinosaurs  Many other plant & animal species  Meteorite hit Earth  Dust, smoke, fires  Temperatures dropped for many years

 “Recent Life” or “Age of Mammals”  Many mammals, birds, insects & flowering plants  Saber-toothed cats, camels, small horses

 Era we are currently living in  Climate changed many times during era  Periods of ice ages  Animals migrate, adapt, or become extinct