AST101H1 Chapter Notes - Chapter 24.1-24.4: Natural Selection, Horsepower, Galactic Habitable Zone

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST101H1
• Professor: Bryan Gaensler

Document Summary

Learn about the history of life through the study of fossils. Most fossils form when dead organisms fall to the bottom of a sea and are buried by sediment. Sediment is produced by erosion on land and carried to sea. Most dead organisms decay and do not leave fossils. Relative time periods are easy to figure --> deeper was formed earlier. Fossil evidence for the early origin of life. Older are rare --> earth is geologically young. Most older life was microscopic (hard to find) Likely took a long time for this processes to evolve. Therefore, photosynthetic life existed some 3. 5 billion years ago. But microscopic life living underground could have survived. May have existed 3. 85 billion years ago, but hard to say. Relatively short time in terms of life span of earth. More offspring than local environment can support with resources. Traits that others don"t have --> better able to compete.