History of life on earth

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History of life on earth

  1. 1. The hisTory ofLife on earTh Evidence of the Past
  2. 2. Fossils Fossils: traces or imprints of once-living things Dead organism is covered by layer of sediment, which presses together to form sedimentary rock
  3. 3. The Ages of Fossils Sedimentary rock has layers, with the oldest layers usually on the bottom and newest on the top Layers where the fossils are found tells a scientist the relative age of fossil Relative dating: Estimating age of fossil by its position in the rock layers
  4. 4. Relative Dating
  5. 5. Absolute Dating When scientists want to determine the age of a fossil more precisely, they use absolute dating to get an exact age Absolute dating: method of measuring age of object in years
  6. 6.  Scientistsexamine atoms, which over time, decay by releasing energy The time it takes for half a sample of atoms to decay is its half-life Scientists measure the ratio of stable to unstable atoms to determine the age of a sample of rock
  7. 7. The Geologic Time Scale Scientists use a type of calendar to divide the Earth’s long history Calendar is divided into very long units of time since the Earth formed so long ago Geologic Time Scale: the standard method used to divide the Earth’s long natural history into manageable parts
  8. 8. Divisions in Geologic Time Scale Divided into eras, which are characterized by the type of organisms that dominated the Earth at that time Precambrian Time: from formation of Earth 4.6 billion years ago to about 543 million years ago  Volcanic eruptions, meteorites, intense radiation from the sun
  9. 9.  Early atmosphere had no oxygen—first organisms were prokaryotes (no nucleus) Cyanobacteria appeared produced own food and released oxygen Ozone layer forms in upper atmosphere and absorbs radiation from the sun
  10. 10.  Paleozoic Era: rocks rich in fossils of animals such as sponges, corals, clams, squids, and trilobites  Fishes appeared, sharks more abundant, forests of giant ferns covered earth
  11. 11. Paleozoic Era
  12. 12.  Mesozoic Era: dominated by dinosaurs and other reptiles, referred to as Age of Reptiles  Firstbirds appeared; flowering plants appeared  By end of era, dinosaurs and many other plants and animal species became extinct
  13. 13.  Cenozoic Era: sometimes called “Age of Mammals”  Mammals included mastodons, saber-toothed cats, camels, and giant ground sloths  Included some periods known as ice ages
  14. 14. Mass ExtinctionsSome of the important divisions in geologic time scale mark times when rapid changes happened on EarthDuring these times, many species died out completely, or became extinctWhen a species is extinct, is does not reappear
  15. 15. Periods when many species suddenly become extinct are called mass extinctionsMost scientists think that the extinction of the dinosaurs happened because of extreme changes in the climate on Earth
  16. 16. These changes could have resulted from a giant meteorite hitting the earth, or forces within causing major earthquakes and volcanic eruptions
  17. 17. The Changing Earth Pangaea -German scientist Alfred Wegener noticed that the continents of Earth look like pieces of a puzzle -proposed that long ago the continents formed one landmass surrounded by gigantic ocean
  18. 18. Wegener called the single landmass “Pangaea” which means “all Earth”
  19. 19. Do the Continents Move? In mid-1960’s, J. Tuzo Wilson came up with idea that continents were not moving by themselves Wilson thought that huge pieces of Earth’s crust were pushed by forces within the planet
  20. 20.  Each piece of crust is called a tectonic plate Wilson’s theory of how the huge pieces of crust move is called plate tectonics
  21. 21.  According to Wilson, outer crust of Earth is broken into seven large plates and several smaller ones Motion of the plates causes continents to move
  22. 22. Adaptations to Slow Changes When conditions on Earth change, organisms may become extinct A rapid change, such as a meteorite impact, may cause mass extinction
  23. 23. Slow changes, such as moving continents, allow time for adaptationEverywhere on Earth, living things are well adapted to location where they liveYet in that location, there is evidence that organisms that lived there in the past were very different
  24. 24.  Example: Animals currently living in Antarctica are able to survive very cold temperatures. But under the frozen surface are the remains of tropical forests Conditions have changed many times during Earth’s history

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