1. Chapter 19
The History of Life

2. The Fossil record Palentologists study fossils
These records provided evidence about the history of life on earth
It shows that different organisms have changed over time
Some even became extinct

3. Interpreting Fossil Evidence
Relative dating- used to determine the age of a fossil
You compare the fossil’s placement in the rock layer with other fossils in the rock
The rock layers are formed by age with the oldest on the bottom

4. Index fossil
Can be used if the species is easily recognized and existed for a short period but have a wide geographic range

5. Radioactive dating
Scientists calculate the age of a sample based ion the amount of remaining radioactive isotopes it contains
The half life is the minimum amount of time it takes for half of a radioactive element to decay

6. Geological time scale Used to divide time
After precambrian time, the basic divisions of the geological time scale are eras, periods, and epochs

7. eras Paleozoic era- 544 million years ago, vert and invert
Mesozoic- 251 million yrs ago, dino and mammals
Cenozoic- 65 million yr ago, mammal age

8. Periods and epochs
Period range in length from 10 million years to less than 2 million years
Further divide periods into epochs

9. Earths Early History
Formation of the earth occurred 8.2 billion years ago
Its early atmosphere contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water

10. First organic molecules
Miller and Urey did an experiment which suggested how mixture of compounds could have arisen from simplier compounds present on primitive earth

11. How Did Life begin? 1. formation of microspheres
2. evolution of RNA and DNA
3. free oxygen in air drove some life forms to extinction and evolved others

12. Origin of Eukaryotic Cells
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by several organisms
After eukaryotic cells arose, those cells began to reproduce sexually
This enabled evolution to take place at a greater rate

13. Evolution of multicellualr life forms
90% of Earth’s history occurred during Precambrian
Simple anaerobic forms appeared and were followed by photosyntheitc forms which added oxygen to the air
Aerobic forms evolved and eukaryotes appeared
Early in Paleozoic era the fossil record became rich with evidence of many types of marine life
Life was highly diverse by the first part of Paleozoic era

14. Cambrian Period This is when diversification of life occurred
Organisms had hard part and first animilia phyla evolved
Trilobites were common

15. Ordovician and silurian periods
Octopus and squid ancestors appeared along with aquatic arthropods

16. Devonian period Animals began to invade the land
Fish developed the ability to crawl on leglike fins
Fish had jaws, bony skeletons, and scales

17. Carboniferous and permian period
Life expanded over the earth’s continents
Other groups of vert evolved from amphibians
Mass extinction occurred at the end of the Paleozoic era
It affects both plants and animals on land and on sea
95% of the complex life in the ocean disappeared

18. Mesozoic era Increase dominance of the dinosaurs
1. triassic period-fish, reptiles insects
2. jurassic period-dinosaurs dominant
3. cretaceous period-reptiles still dominated, but another mass extinction occurred

19. Cenozoic era
Mammals evolved adaptations that allowed them to live in various environments

20. Patterns of evolution
Macroevolution- large scale change that take place over a long time
There are 6 important patterns to macroevolution:
1. mass extinction
2. adaptive radiation
3. convergent evolution
4. coevolution
5. punctuated equilibrium
6. changes in developmental genes

21. Mass extinction
Causes food webs to collapse

22. Adaptive radiation
Unrelated organisms come to resemble one another

23. coevolution
The process by which 2 species evolve in response to changes in each other over time
Ex flowering plants

24. Punctuated equilibrium
Patterns of long stable periods interrupted by brief periods of more rapid change