A history including how life evolved, how the geosphere changed and major extinction events.

 Eons ◦ Eras  Periods  Epochs

 Earth is approximately 4.6 billion years old.  Remember: ◦ How did Earth form? ◦ How are elements arranged?  Earth began to cool ◦ 4 billions years ago: rocks ◦ 3.8 billions years ago: water

 Could organic molecules form in Early Earth?  Miller and Urey experiment

 Geologic evidence suggests that about 200 to 300 million years after earth cooled enough to carry liquid water, cells similar to modern bacteria were common.  How did these cells originate? ◦ Microspheres ◦ Evolution of RNA and DNA

 The first organisms were single celled prokaryotic anaerobic cells that resemble modern bacteria. ◦ Evidence: microscopic fossils in rocks that are more than 3.5 billion years old.  Photosynthetic cells! ◦ How did the oceans go from brown to blue-green? What color is the sky now?

 Endosymbiotic theory

 How did live begin to evolve into diverse life? ◦ Asexual versus sexual reproduction ◦ Multicellularity

 Periods: ◦ Cambrian: “Cambrian explosion”, hard parts, shells, outer skeletons, invertebrates, arthropods. ◦ Ordovician and Silurian: aquatic arthopods, fishes, first land plants, octopi and squid. ◦ Devonian: land plants, insecnts, vertebrates, sharks, “age of fishes”. ◦ Carboniferous (Mississipian/Pennsylvanian) and Permian: amphibians, reptiles, winged insects, ferns.

 Most organisms lived in the sea at this time.  The sea level dropped caused by plate tectonics.  The majority of land mass was over the south pole at this time and was a large glacier.  Approximately 57% of Earth’s species went extinct at this time.

 The third extinction event occurred at the end of this period.  It was caused by ◦ fluctuating sea levels because more glaciers pulled water from the oceans. ◦ and global cooling due to land plants removing CO2 from the atmosphere.  There was approximately a 50% extinction of the species on Earth.

 This is the fourth extinction event.  It is often called the “Great Dying” event and was caused by: ◦ Eruption of Siberian Volcanoes ◦ Formation of Pangaea disrupted ocean currents ◦ Possible meteor impact  This resulted in an 83% extinction event ◦ About 96% of all marine species ◦ About 70% of all land vertebrates ◦ Many arthropods and land plants also died.

 Periods: ◦ Triassic: “Age of reptiles”, fishes, insects, cone breaing plants, mammals/ ◦ Jurassic: dinosaurs, birds. ◦ Cretaceous: dinosaurs, birds, leafy trees, shrubs, small flowering plants.

 This is the fifth extinction event  Caused by the eruption of the central Atlantic province. ◦ Sulfur gas blocked the sun ◦ Large amount of lava released over several centuries.  This was a 48% extinction and a majority of the species that went extinct were marine ◦ Ammonites ◦ Corals ◦ Seed ferns

 At the end of the cretaceous period there was a sixth mass extinction event.  It is often referred to as the “K-T Boundary” and was likely caused by ◦ Pangaea breaking up, ◦ Eruption of Deccan Volcanoes in India ◦ And possibly an asteroid impact.  It marks the end of the cretaceous period/Mesozoic era, the “age of reptiles” (dinosaurs).

 Periods: ◦ Tertiary: marine mammals, grasses, large mammals ◦ Quarternary: humans

 73,000 years ago there was an event that led humans to near extinction.  It was caused by the Toba super volcano on the island of Sumatra. It disrupted ecosystems on a global scale.  Only a few ‘pockets’ of individuals remained, estimated at around 10,000 total.