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Fossils are the remnant or traces of a dead and decaying organism that can be found in stratified rocks.They are the mineralized form of an organism formed from bones and shells that cannot decay easily.

They provide preserved evidence that life existed from a past geological age, including remains and impressions of an animal or plant that has been embedded in Earth鈥檚 crust.

The rich source of fossils is sedimentary rock. The fossil record depends on many horizontal layers called strata,in which fossils have aggregated in sedimentary rock layers.

Sedimentary layers are arranged on one another over a long exposure, and sedimentary rock is formed by squeezing the weight of the top layers on the lowest layer.

The fossil鈥檚 age is estimated by radiometric dating methods,depending on the natural radioactive decay of radioactive isotopes such as carbon or potassium. It is not influenced by temperature, pressure, climate, and rainfall, and the rate of decay is determined by half-life.

For example, the half-life of Uranium-238 is 4.5 billion years due to slow decay.

Examples of the fossil records are stratified rocks exposed in the walls of the Grand Canyon, complex plants, and animals evolving from the unicellular organism showed that life on Earth was once different from today鈥檚 life on the planet.