Fossils An Introduction The Theory of Evolution by

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: – Earth’s 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

• Radioactive dating is used to measure rocks, and fossils found in them: • The mathematical expression that relates radioactive decay to geologic time, is: – D = D 0 + N(eλt − 1) where – t is age of the sample, D is number of atoms of the daughter isotope in the sample, D 0 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 λ 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. • Earth’s geological history is long and complex… it is divided into hundreds of different eras, ages, epochs, etc. Geological Time

So… we’ve 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, 000 s 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