I think A is the youngest layer, because of the new sediments that fell upon the animal.
Nitrogeneous bases
sugar
phosphate group
The fertilized cell that results is referred to as a zygote. A zygote is diploid cell, which means that it has twice the number of chromosomes as a gamete
Oxygen.
Oxygen was fatal when organisms started using photosynthesis, this event was known as the Great Oxidation Event.
