Fossils: An Introduction The Theory of Evolution by Natural Selection Evolution is a theory (set of related, well-supported hypotheses) that explains the diversity of living organisms alive today and those that have lived before. Natural selection is the mechanism by which that theory proposes species change over time, form new species, and sometimes go extinct. The support for evolution by natural selection includes 2 major lines of physical evidence: Earths fossil record Genetics Evolution is a theory (set of related, well-supported hypotheses) that explains the diversity of living organisms alive today and those that have lived before. Natural selection is the mechanism by which that theory proposes species change over time, form new species, and sometimes go extinct. The support for evolution by natural selection includes 2 major lines of physical evidence: Earths fossil record Genetics Fossils Fossils are the preserved remains or traces of ancient organisms. Types of Fossils Permineralization: the most common way fossils are made. Remains are covered by sediment and compressed and mineralized into rock. Other Types of Fossils Amber Ice Trace fossils Many more A Taste of Geology Fossils are found only in sedimentary rocks. As soil and rocks are weathered, particles called sediment build up at the bottom of the water. Increased pressure crushes the particles together, making sedimentary rocks Law of Superposition The oldest rocks are on the bottom of the column, the newest rocks are on top Geological Time Radioactive dating is used to measure rocks, and fossils found in them: The mathematical expression that relates radioactive decay to geologic time, is: D = D0 + N(e t 1) where t is age of the sample, D is number of atoms of the daughter isotope in the sample, D0 is number of atoms of the daughter isotope in the original composition, N is number of atoms of the parent isotope in the sample, and is the decay constant of the parent isotope, equal to the inverse of the radioactive half-life of the parent isotope[14] times the natural logarithm of 2. Earths geological history is long and complex it is divided into hundreds of different eras, ages, epochs, etc. So weve got Fossils, and We Know How Old they Are We can combine these two things to figure out the history of life on Earth!!! Phylogenetic Trees Phylogenetic trees are used to represent the most probable evolutionary relationships between a group of organisms. They can be based on Genetics Fossils Morphology (structure) Two types of Evolution are Found in the Fossil Record Gradual evolution is slow change over long periods. Punctuated equilibrium means big changes can happen fast (in geology, fast means 100,000s of years!) How do species change over time? Phyletic speciation: gradual changes in a single species Divergent Speciation: one species splits into two or more. Both types appear in the fossil record