Evidence for evolution

• Some of the best evidence scientists have about the history of life on Earth comes from fossils
• Fossils are the remains of organisms from millions of years ago that are found preserved in rocks, ice, and other places
• Fossils have revealed the world of dinosaurs, giant reptiles that dominated the Earth at one stage and died out many millions of years before the evolution of the first human beings
• Fossils


  • Can be formed when an animal or plant does not decay after it has died due to lack of oxygen, poisonous gases, or low temperature
  • Can be formed when harder parts of the animal or plant are replaced by minerals as they decay and become part of the rock
  • Can be mould fossils formed when an impression of an organism is made in mud and then becomes fossilised
  • Can be cast fossils made when a mould is filled in
  • Rock fossils are the most common form
• The fossil record is not complete for several reasons: many of the very earliest forms of life were soft-bodied organisms, most organisms that died did not become fossilised, and many fossils are still to be found
• The fossil record helps scientists to understand how much organisms have changed since life developed on Earth, but this understanding is often limited due to the incomplete nature of the record
• Relatively complete fossil records, such as for the horse, can show how some organisms have changed and developed over time and help reconstruct the ecology, climate, and environment of millions of years ago
• Fossils also show that not all animals have changed very much, such as sharks which evolved early into a form that was almost perfectly adapted for their environment and way of life