it is testable
Note the word science in that last sentence. Earth Science is a science, or maybe its made up of a lot of sciences. But what is science? Most people think of science as a bunch of knowledge. And it is. But science is also a way of knowing things. Its different from other ways of knowing because it is based on a method that relies on observations and data. Science cant say how many angels can dance on the end of a pin because that question cant be tested. In fact, science cant even say if there are such things as angels for the same reason. For something to be science, it must be testable. And scientists are the people who do those tests.