Question

some preserved traces of living organisms usually on the hardened mud found in the deep layer of the earth are usually known as

Answer 1

A trace fossil , also called an
ichnofossil is a geological record of biological activity. It leaves traces of any impression that has been made by an organism. In regard to this, it would be easy to see the footprints of an organism even if the said movement occurred hundred of years ago. The remains is not just limited to the footprints but also extend to other organic materials produced. Fossils therefore preserved remains of once-living organisms.

Answer 2

The preserved traces of living organism which are found on the hardened mud in the deep layer of the earth are usually known as "Trace Fossils" .
Explanation:
A trace fossil consists of an imprint or a mark left by an organism, as opposed to physical remains. Trace fossils are produced in soft sediments and include surface tracks, molded impressions left by organisms, or tissues that later decayed and subsurface burrows or tunnelings.
Trace fossils are formed if two conditions are met. First, the activity has to take place in a material that will hold its form. Second, the evidence of the activity has to be well-preserved often by being buried quickly.