The layer where organisms can exist on the surface of the Earth is called the biosphere.

Here's why:

* Biosphere: This term encompasses all the living organisms and their environments on Earth. It includes the Earth's surface, the atmosphere (to a certain extent), and the upper layers of the Earth's crust.

* Other layers: While the Earth has other layers like the lithosphere (crust and upper mantle), hydrosphere (water), and atmosphere (air), these layers don't specifically define where life can exist.

So, the biosphere is the only layer that specifically encompasses all living things and their environments.