Earth, Extinction, and Evolution The History of Life

Formation of Earth Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, & water

The First Organic Molecules Experiments have suggested how simple compounds found on the early Earth could have combined to form the organic compounds needed for life

Free Oxygen The rise of oxygen in the atmosphere drove some life forms to extinction Others evolved new, more efficient metabolic pathways that used oxygen for respiration

Mass Extinction Mass extinction - when many types of living things become extinct at the same time Extinct - the species died out At the end of the Paleozoic Era, a mass extinction affected both plants & animals on land & in the sea 95% of life in the oceans disappeared

Origin of Eukaryotic Cells Endosymbiotic theory - proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms

Evidence of Evolution The Fossil Record: Darwin noticed that the sizes, shapes, & varieties of related organisms preserved in the fossil record, changed over time

Evidence of Evolution Geographic Distribution of Living Species: Darwin realized that similar animals in different locations were the product of different lines of evolutionary descent

Evidence of Evolution Homologous Body Structures: Homologous structures - structures that have different mature forms but develop from the same embryonic tissues Not all homologous structures serve important functions Organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs

Homologous Structures

Evidence of Evolution Homologous Body Structures: Vestigial organs - may resemble miniature legs, tails, or other structures, a trace of a homologous structure

Evidence of Evolution Similarities in Early Development: The early stages or embryos, of many animals with backbones are very similar

Patterns of Evolution Extinction: More than 99% of all species are now extinct It usually happens for a reason; species compete for resources, & environments change Some species adapt & survive, others become extinct

Patterns of Evolution Adaptive radiation - when a single species has evolved, through NS, into diverse forms that live in different ways Ex.) Darwin’s Finches

Patterns of Evolution Punctuated equilibrium - a pattern of long, stable periods interrupted by brief periods of more rapid change

Summary of Darwin’s Theory Individual organisms differ, & some of this variation is heritable Organisms produce more offspring than can survive, & many that do survive do not reproduce

Summary of Darwin’s Theory Because more organisms are produced than can survive, they compete for limited resources Individuals best suited to their environ., survive & reproduce most successfully

Summary of Darwin’s Theory These organisms pass their heritable traits to their offspring This process of NS causes species to change over time

Summary of Darwin’s Theory Species alive today are descended with modification from ancestral species that lived in the distant past This process, where diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life