To SUM it up I hope we found evidence of one of the following.

  - Evidence of Oceans on Mars
  - Nitrogen in the soil, needed for plants to grow on mars
  - Amino Acids
  - Fossils

It could be something that is a play on words, 'Earth Shattering' could mean volcanic activity

I also wonder if they are finding rare minerals or metals.

It could also have to do with Isotope ratios, as much of our history currently depends on Carbon Dating and other Radioactive Isotope decay rates. Different Atmospheric conditions could have different isotope ratios, this would be a pretty big shake up and it does not necessarily require the rover to find a specific chemical or a complex thing like DNA or organism remnants.

My mind would be blown, if NASA found one of the following.

  - living plants
  - living microbes
  - manufactured materials not of human/ earth origin.
  - tons of precious metals.