Geologic Time Scale.Scientists decide when an era begins<span> and </span>ends<span>, due </span>to<span> mass extinction. ...</span>Scientists determine<span> when drastic changes </span>are<span> made by the fossil record, which shows earths past organisms that have become extinct.</span>
Answer:
Embryogenesis is the development of an animal or plant embryo.
OR
Embryogenesis is the process of development of an embryo from zygote. In embryogenesis, the zygote undergoes repeated cell division through mitosis. The divisions help in the growth of an embryo. Cells undergo differentiation attaining specific shape, size and function. Cell differentiation occurs at specific location resulting in the production of different tissue, organs and organ system.