What are Fossils?

Fossils are the preserved remains or traces of animals, plants and other organisms from the remote past. They are formed by a continuous process of burying and decomposition over a certain period. 

Fossil formation:
  • Some invertebrates living on the sea bed died and were buried in the sand.
  • More sand was accumulated and formed sandstone under pressure.
  • After millions of years, dinosaurs living in the area died and their bodies were buried in the mud.
  • The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils.
  • Again millions of years later, the bodies of horse-like creatures dying in the area were fossilized in the rocks above the earlier rocks.
  • Much later, because of erosion and water flow, some rocks wore out and exposed the horse-like fossils.

Two methods to determine the age of fossils:

  • When dug into the Earth, the fossils closer to the surface are more recent as compared to the fossils found in deeper layers.
  • The fossils can also be dated by detecting the ratios of different isotopes of the same element in the fossil material. This process is known as radiocarbon dating. When living organisms change into fossils, their rate of radioactive C14 decay decreases slowly. In this way, the age of fossils can be determined with the help of radioactive C14.

Two roles of fossils in tracing evolutionary relationships:

  • To tell us about the similarities between two species
  • To provide links between two groups indicating that perhaps one species evolved from the other

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