Scientists establish the age of a rock or fossil based on natural radioactive decay and certain elements such as potassium and carbon, this is used to make reliable “clocks” to date ancient events.
(Sorry if not all is accurate hope it helps)
The answer is stem cells, they consist of classes of cells
that are undifferentiated and are able to be classified them into types like
specialized cells. They consist of having two main sources that will help them
develop and mature, these main sources are called the embryonic stem cell and
the adult stem cell.
I think that it is atmosphere but not 100% sure you might want to double check
I believe that the food web is more stable
