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Evidence of the History of LIFE

Evidence of the History of LIFE. How do scientists know evolution has occurred?. Who looks for the evidence?. Paleontologists: scientists who study fossils Geologists: scientists who study rock layers. Fossil Evidence. Fossils can tell us Structure of an organism What the ate

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Evidence of the History of LIFE

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  1. Evidence of the History of LIFE How do scientists know evolution has occurred?

  2. Who looks for the evidence? • Paleontologists: scientists who study fossils • Geologists: scientists who study rock layers

  3. Fossil Evidence • Fossils can tell us • Structure of an organism • What the ate • What ate them • What environment they lived in All this information of past life groups organisms together by the order in which they lived (oldest to recent. This is called the FOSSIL RECORD. • The fossil record can show how different groups of organisms changed over time

  4. Fossil Evidence cont’d • Life on Earth has changed over time, which is evident in the different fossils found in different rock layers

  5. Relative Dating: “Law of Superposition” • Where the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock • Rock layers form in order by age, with oldest at the bottom, and newest on top, closer to the surface. • Paleontologists can also use index fossils to compare relative ages. To join the index, a species must be (1)easily recognized, (2)existed for a short period of time, but (3)had a wide geographic range.

  6. Radioactive Dating • Allows scientists to assign absolute ages to rocks. • Radioactive elements decay into nonradioactive elements at a steady rate, unique to that element • This type of dating is measured in the half-life of radioactive atoms (the length of time required for half of the sample to decay)

  7. To Summarize… Relative dating estimates the age of a fossil by comparing it with other fossils, while radioactive dating is a precise calculation of the age of a sample based on the amount of remaining radioactive isotopes it contains.

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