(need fast)which unit of geologic time is the oldest?
a)cenozoic
b)mesozoic
c)ordovician
d)precambrian

D) Precambrian

Explanation:

Option D, Precambrian​

Explanation:

Cenozoic period existed some 65 million years ago when the largest animal species evolved on planet earth. Mesozoic is a period that existed just before the Cenozoic period and lasted from 252 to 65 million year ago. Ordovician period started some 485 million years ago and existed between the Cambrian and Silurian period. Pre Cambrian period occurred some 4600 million years ago.  

Hence, Pre Cambrian period is the oldest geological time  

Option D is correct.

1. amino acid refers to the fundamental building block of proteins, comprising of an amino group and a carboxyl group.

2. catalyst refers to any substance, which increases the rate of chemical reaction without being used up in the reaction.

3. a complex molecule containing he genetic code is dna or deoxyribonucleic acid.

4. an enzyme refers to a molecule of protein, which is unique in accelerating up a particular chemical reaction in the biological systems.

5. nucleic acid refers to an sequence of sugars, phosphates, and nitrogenous bases, for example, dna and rna.

6. a protein refers to a large, composite organic molecule comprising of a huge number of amino acids associated together with the of peptide bonds.

7. rna refers to a nucleic acid that takes part in the production of proteins.

8. substrate refers to a compound, which takes part in a chemical reaction, and is chemically modified by the reaction.