1. History of the Earth Chapter 12

2. How Old is the Earth?  Early Earth  4.5 Billion Years Old  Before then it was a fiery ball of molten rock.  The water vapor from the atmosphere cooled and formed vast oceans.

3. How Old is the Earth?  How do we know?  Evidence of the earth’s age can be found in rock.  Radiometric Dating  The estimation of age of an object by measuring its content of radioactive isotopes.

4. Radioactive Decay  Radioactive Decay  Radioactive isotopes are unstable isotopes that break down giving off energy in the form of radiation.

5. The Evidence of Evolution Fossils –Preserved or mineralized remains or imprint of organism that lived long ago –Show a pattern of development form early ancestors to now

6. Evidence of Evolution Most scientists agree that: 1.Earth is about 4.5 billion years old 2.Organisms have inhabited Earth for most of its history 3.All organisms living today share common ancestry with earlier, simpler life-forms.

7. Evolution of Cellular Life Precambrian Era –The first bacteria have been found to have lived 2.5 billion years ago during this era –Cyanobacteria First prokaryotes First organisms to live on earth Photosynthetic bacteria Released oxygen into the atmosphere –Protists First Eukaryotes Large group of unicellular and multicellular organisms

8. Evolution of Cellular Life Cambrian Period –About 1 billion years ago –The first animals probably originated from this period –This great diversification of animals is called the “Cambrian Explosion”

9. Evolution of Cellular Life Ordovician Period –About 505 to 438 million years ago –This is the time when animal diversity abounds and the first jawless fishes swam the seas –The appearance of more sea animals occurs during this period Mass Extinction –During this period a large percentage life on earth went extinct

10. Evolution of Cellular Life Silurian Period (437 million years ago) –During this period Plants, arthropods, and fungi invade the land May have been the first multicellular organisms to actually live on land. Jawed fishes appear in the seas Devonian Period (405 million years ago) –During this period bony fishes become abundant –Amphibians The first vertebrates to leave the sea –Second Mass Extinction

11. Evolution of Cellular Life Carboniferous Period (360 million years ago) –Reptiles who evolved from amphibians have begun to inhabit the earth Permian Period (290 million years ago) –Third Mass Extinction Triassic Period (250 million years ago) –The first dinosaurs and Mammals appear –Fourth Mass Extinction

12. Evolution of Cellular Life Jurassic Period (210 million years ago) Cretaceous Period (150 million years ago) –This period is marked by the appearance of flowering plants –Fifth mass extinction

13. Evolution of Life Tertiary Period (65 million years ago) –Due to the continents drifting birds and Mammals spread –Major mammal groups evolve and become abundant on land –Appearance of Australopithecus

14. Evolution of Cellular Life Quarternary Period (5 million years ago–today) –During this period the first Homo sapiens walked the land and continue to this day.