1. Earth, Extinction, and Evolution
The History of Life

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

3. 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

4. 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

5. 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

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

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

8. 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

9. 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

10. Homologous Structures

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

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

13. 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

14. 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

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

16. 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

17. 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

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

19. 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