Answer: The dead remains of the plants and animals that are burried millions of years ago, are known as fossils. It can be plant fossil or animal fossils.
To convert into a fossil, it is very difficult and rare. In order to be a fossil, hard parts of an organism must be present, that does not get altered. Most of the organism are comprised of soft bodies, so the organism after their death, decays and the soft parts gets removed after coming in contact with the atmospheric oxygen.
In order to be a fossil, hard parts must be present, quick burial should take place, reducing environment should be present. when this conditions are fulfilled then a dead organism or plant, after millions of years, can convert into a fossil. But in nature, it is not always favorable, so we don't get 100% accurate record of a fossil.
