Chapter 19 The History of Life

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mass extinction Causes food webs to collapse

Adaptive radiation Unrelated organisms come to resemble one another

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

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