Viruses can have four different types of nucleic acid. Which two types are not found in living things?

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Asquirrel population lives in an area. over many years, a river in that area grows wider and stronger, eventually forming a canyon. the squirrel populations on the two sides of the canyon can no longer mate with each other and ultimately form distinct species. this is an example of

Why does the earth spin slowly, not faster? is it possible to prove it scientifically? can you prove it with math?