From approximately 240 to 66 million years ago, dinosaurs dominated most of the land habitats on Earth. Around 66 million years ago, most dinosaurs went extinct when an asteroid struck the Earth. Mammals, which were much smaller and lived primarily in underground habitats, were able to avoid extinction. Mammals then underwent an adaptive radiation to develop a wide variety of new species.

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not: both offer magnification to the atomic level.

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.