The Fossil Record
Fossils can be dated to approximate the age of the Earth. Fossils found in stromatolites indicate that Earth is 3.5-4.8 billion years old.
The Origin of Life on Earth
If we assume life did not result from a seeding event from an asteroid or other interstellar body, then life had to have developed from inorganic materials. However, spontaneous animation to form life from non-life does not happen today. This could be due to the atmosphere environment is very different. Urey & Miller designed an experimental model of early earth atmosphere, in which organic molecules can be synthesized from inorganic molecules. With pre-biotic conditions set, Proto-life may occur according to many hypotheses: Organic compounds form polymers of repeating units, lipids & others can and do organize into spheres based on inherent properties. The lipid spheres can encapsulate organic molecules; the encapsulated organic molecules such as RNA can then self-replicate, are autocatalytic, and can act as rudimentary templates for protein synthesis. Competition for scarce resources such as RNA monomers leads to natural selection of fittest RNA molecule, resulting in reproduction of that RNA molecule. The next biggest event occurred when prokaryotes formed. Then prokaryotes photosynthesized to produce oxygen into the environment. Oxygen in the atmosphere started protists, the first eukaryotes. Eukaryotic life next led to multi-cellular life on Earth.
The Major Eras
The major geological eras of Earth are: Precambrian Time, the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. Precambrian time is when life first appeared, and when most of original life evolved. In the Paleozoic Era is when life in the sea became very diverse, and vertebrates appeared. The Mesozoic Era is the age of reptiles, such as dinosaurs. The current Era, the Cenozoic is the age of mammals.
Evolutionary Patterns
Extinction is the first obvious evolutionary pattern. Extinction occurs when all of the individuals of a species die, so that the species can no longer reproduce. Adaptive radiation is when there is an explosive amount of change in a short time leading to many new diverse species. Convergent evolution occurs when organisms which have to survive in similar environments develop similar body parts over time, although evolutionarily the organisms are unrelated, such as a penguin and a fish. Coevolution occurs when two species depend on each other for survival, and when one evolves, the other evolves with it. Puncuated equilibrium is the theory that evolution occurs in bursts followed by slow, stable periods, rather than gradual constant change.
