Early Earth History Precambrian Time • Precambrian Time consisted of the Hadean, Archean, and Proterozoic Eras. • Lasted from 4.5 billion to 544 million years ago. • Longest interval of geologic time • During the first billion years there were no life forms and it was probably just volcanoes erupting and little else. Not much is known about life forms of this time because: • Precambrian rocks have been so deeply buried that they have been changed by heat and pressure. Fossils cannot withstand these conditions. • Precambrian fossils didn’t have hard parts that would have increased their chances of being preserved as a fossil. • Rocks older than 3.5 billion years are rare due to remelting and erosion. Early Life • Stromalites are layered mats formed by cyanobacteria colonies. • Cyanobacteria- blue-green algae thought to be one of the earliest forms of life on the Earth. • Appeared 3.5 billion years ago • Have chlorophyll and carry on photosynthesis. Cyanobacteria cont. • Through photosynthesis oxygen is produced and released into the atmosphere. • The ozone layer then formed providing shielding of ultra violet rays from the Earth allowing species of one-celled organisms to evolve into more complex organisms. Precambrian Fossils • Invertebrates: animals without backbones • Appeared toward end of the Precambrian Time • Because they had soft bodies they did not leave many fossils. • Most Precambrian fossils are trace fossils. Ediacaran Fauna • Animals shaped like jellyfish, worms and soft corals lived in the late Precambrian Time • Fossils of these organisms were first found in the Ediacara Hills in southern Australia thus the name Ediacaran Fauna. • These were bottom dwellers and had tough outer coverings like air mattresses. • Scientists are not sure why they became extinct, it may have been the Trilobites outcompeted them. Paleozoic Era • The era of ancient life, went from 544 to 248 million years ago. • Traces of life forms are much easier to find in Paleozoic rock than in Precambrian rock. • An abundance of animal with hard parts marks the beginning of the Paleozoic Era. • Warm shallow seas covered large parts of the continents during this time period. Paleozoic Era Cont. • Much of the life was marine (ocean dwellers). Trilobites were common especially early on • Other life forms developed shells therefore, the fossil record of this era contains abundant shells. • Vertebrates (animals with backbones) evolved during this era as well. Paleozoic Life Cont. • The first vertebrates were fish like animals without jaws. • Armoured fish with jaws lived during the Devonian Period. Some were large enough to eat large sharks with their powerful jaws. • Forests appeared on land by the Devonian Period and vertebrates began to adapt to land environments. Life on Land • Many fish had lungs and gills allowing them to live in water with a low oxygen content. They could swim to the surface and breathe air. • One kind of ancient fish had lungs and leglike fins to crawl around on the ocean floor. Paleontologists believe it may have evolved into amphibians Pennsylvanian Period • Amphibians evolved an egg with a tough skin that wouldn’t dry out, these animals became the reptiles and they no longer needed water to reproduce. • Reptiles also have scales that help prevent water loss so that they could live farther away from water where amphibians could not. Mountain Building • Several mountain building episodes occurred during the Paleozoic Era. • Appalachian mountains formed in several stages: • First the ocean separating Europe and Africa from North America closed. The volcanic island chain that had formed in the ocean collided with the North American Plate generating mountains. Mountain Building Cont. • The next mountain-building episode resulted from the African Plate colliding with the North American Plate. When this occurred rock layers were folded and faulted. • Rocks were pushed as much as 65 km westward by the collision. • Sediments were uplifted to form an immense mountain belt, some of which remains today. End of Paleozoic Era • More than 90% of marine species and 70% of all land species died off. • One explanation is a change in climate and a lowering of sea level. • Near the end of the Permian Period the supercontinent Pangaea formed. Glaciers formed over much of its southern part. • As continents continued to collide mountains were formed and seas closed, while deserts spread over North Amer. and Europe. Many organisms especially marine organisms became extinct. Other Theories About Extinction • Volcanic activity may have been great enough to have affected the entire globe. • A large asteroid or comet collided with the Earth some 248 million years ago. This is also the theory that explains the worldwide extinction at the end of the Mesozoic Era. • Could have been a combination of some or all of these events happening about the same time.