If scientists discovered a lokiarchaeota cell sample, how would it them determine whether their theory is correct?

If the scientists did find an actual preserved cell, they will be able to look at the structures, which will add further evidence to their theory. They can then use their findings and compare them to other eukaryotes to trace an evolutionary lineage. (This is the exact answer given by the system.)

1. is geographic distribution

2 is increasing complexity

3 is transitional forms