[en-us]

We can sequence its DNA and see how similar it is to the ones on Earth. If there are living organisms on the moon that share a common ancestor with Earth tardigrades then they diverged a very long time ago and their DNA will reflect that. But if their DNA is identical to those on Earth then we know they came from Earth.

[dwiel]

Do you know how much tardigrades DNA have changed since they first appeared on earth?

[en-us]

I do not know exactly how much but this is something that can be approximately quantified.