BBC: Learnig lessons from the Moon- 2

That's right. Astronomers know that comets are full of ice, and think comets brought water to Earth when they crashed into it. Evidence of those crashes has been erased by the constantly moving surfaces on Earth, but not on the Moon. 

So, comparing water from the Moon with water on Earth could provide scientists with vital information, as Dr Smethurst explained to BBC Radio 4's, Inside Science:

So they'll be looking essentially to see if it has the same characteristics as water here on Earth, and then we can sort of trace that back from sort of the crater history as well to working out what actually happened. How long has it been there for as well. Also, various other minerals that might be there, these very heavy minerals that we know come from comets and asteroids. Again, that would be this sort of smoking gun to be like, yes this that's where this water came from and it's likely that Earth's water came from there as well. 

Scientists can trace the existence of water on the Moon back to find out what happened on Earth. If you trace something back, you discover the causes of something by investigating how it developed. 

For this reason, Dr Smethurst says finding water on the Moon would be finding a smoking gun, a modern idiom meaning indisputable evidence or proof. We've learned a lot about the Moon, but we still don't know the answer to your question, Neil- who was the third Apollo astronaut on that famous first landing in 1969? I said it was Michael Collins...

Which was...the correct answer! Michael Collins never set foot on the Moon himself, but afterwards said the experience of looking back at Earth from the Apollo spacecraft changed his life forever. OK, let's recap the vocabulary we've learned from our trip to the Moon, starting with inert, not moving or unable to move. 

A crater is a very large hole in the ground. 

Pockmarked means marked by small holes and scars. 

If you say something is a big deal, it's important or significant in some way. 

To trace something back means to discover its causes by examining how it developed. 

And finally, the idiom a smoking gun refers to indisputable evidence or conclusive proof of something. Once again, our six minutes are up. Join us next time for more scientillating science and useful vocabulary here at 6 Minute English.

inert- dull, slow, dim, gross

whereas- compared with the fact that or but