Why do you think that astronomers are considered to be earth scientists?

Astronomers are those that study the galaxies, the solar system, and planets and how they have originated and evolved right after their formation.

Astronomers are also considered to be the earth scientists because the earth itself is a part of the milky way galaxy that orbits around the sun in an elliptical manner like other planets of the solar system. And they have contributed a significant amount of information helping us to understand how the various processes take place in the outer space, their important controlling factors and their planetary interaction with each other. Earth science and astronomy are related to one another in multiple ways.

For example, most of the rocks found on earth are from the outer space and since they are found on earth's surface or beneath it, the astronomers as well as geologists are required to study these celestial objects.

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.