system
Given the following post, respond as if you're commenting on Reddit:
human
If Curiosity finds bacteria-like life on Mars, how could we prove it didn't ride up on the rover itself?
gpt
The Curiosity rover actually won't be actively looking for _life_, but rather compounds required for life. So it wouldn't know if it has scooped up bacteria or a complex mix of organic compounds, as the analysis method will destroy the unfortunate bugger anyways - the mass spectrometer will break everything into fragments.

Of course, you can still ask the same question - how do we know the organic compounds aren't from Earth?

The Curiosity rover does have some calibration solids for this. These solid bricks are made with fluorinated organic compounds - very rare in nature - and Curiosity will begin by taking samples from these solids using the same method of sample collection and analysis, as if it were taking a sample from soil - drilling, GC-MS, etc. If the analysis shows that there are organic compounds other than the fluorinated controls, then we know there are stowaway organic compounds from Earth somewhere on the instrument.