What do scientists use to mark boundaries in the geologic time scale?

Era is used to mark the boundaries of geological time scale by using radio carbon dating technique.

Explanation:

Geological time starts with Precambrian time.

Geologically, time is divided between the Precambrian era and present time into era.

The three eras are Paleozoic era, Triassic period and Cenozoic era.

Era is further divided into periods.

Scientists use radio carbon dating to study fossils and rock formation. With this study they were able to divide them in exact geological scale.

Geologic scale is the record of events in earth's history and evolution.

it has one origin of replication, but it proceeds in two directions - d)

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.