Question

What are fossils? How are they formed? Explain how fossils support evolution.

Answer 1

Fossils: Fossils are the naturally preserved remains of organisms like plants and animals that existed on the earth a long time ago but got buried or extinct.

Formation of fossils:

• Fossils usually form when the organisms get buried due to different reasons.
• The bodies or remains of the organisms then get covered by ashes, lava, sand, or soil to form layers over them.
• These layers get hardened over time due to different factors like pressure.
• Each layer indicates the geologic time during which these organisms got buried.

Example of formation of fossils:

• The organisms like invertebrates that once lived in the oceans, got buried in the sand after their death.
• Later, their bodies were covered by the sand. The sand kept accumulating over them and this created a layer.
• The remnants of the invertebrates stayed in this layer and got preserved. The pressure then made sandstone.
• Later, after many million years, dinosaurs got extinct, their dead bodies were then buried in the same manner.
• The bodies of the dinosaurs got buried at a higher level, they were buried at a lesser depth/distance from the surface of the earth.
• Their fossils are therefore present closer to the surface of the earth as compared to the invertebrates that got buried earlier than the dinosaurs.
• Similarly, again after many million years, organisms that looked like horses died and got buried above the dinosaurs.
• These organisms also got buried in the layers and fossilized.
• Later, due to many reasons like erosion by the rainfall, the fossils of the horse-like organisms got exposed.

Evolution: Evolution is the process of accumulation of genetic differences in the living organism over the period and generating new varieties of living organisms.

Evidence of evolution- Evolution of birds:

• The fossils help in tracing the particular time when the organism was living. For example, the depth at which the fossil is found is related to the period during which the fossil (organism) lived.
• The fossils provide the order of evolution of different species over time.
• Example: Archeopteryx is an example of a fossil that has features of both birds (have feathers) and reptiles (have a long-tail).
• This fossil represents an interlink between birds and reptiles.
• This concludes that the birds have evolved from reptiles.