Because they are the essential micronutrients for the different metabolites of living organisms?
The remains are called fossils. Fossils are remnants of animals, plants, or microorganisms that have been solidified in the process of fossilization, where the organism is surrounded by sediment, minerals, and other solid objects which are compressed and heated around the organism over time. This forms a solid mass with the preserved organism inside, other known as a fossil.
The limbic cortex. Another area called the precuneus also plays a role.
DNA structure. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).