They make a lot of assumptions, based on what they know about today
Kind of like... coffee is bad for you; coffee is good for you. Chocolate is bad for you; Chocolate is good for you.
Assumptions should always come with disclaimers, especially if “Scientist” or “Doctor” is in your name somewhere.
“Doctor, my stomach hurts!” “Well, sir,” said the doctor. “I assume you could have swallowed an anvil. Here, let me slice you open and see.”
I’d like a little more testing first, please.
Hm, let’s see, the Moon has been slowly receeding from Earth, Earth has an active magnetic field, the Moon would have spent lots of orbit time moving through the magnetic field of the Earth ... well, they are paid to guess I suppose.