Heredity and Evolution — Science STD 10 — Question

Fossils are the remains of plants, animals or other organisms which are in petrified form. These are formed when plants or animals buried in mud and soil. The soft tissues decay easily by leaving the hard bones and shells. Over a period of time sediment builds over these bones and shells, then hardens to form rock.
Fossils provide direct evidence for the history of evolution. Fossils help scientists to correlate the organisms from the past and present. Calculating the age of fossils gives idea about the occurrence of organism in a particular period.