Life arose very quickly on Earth after it cooled down. Photosynthesis took longer and Eukaryotic life took longer still. Seeing a Martian protozoa that evolved independently of Earth life would be scary. Bacterial mats around a thermal vent not so much.

https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...

EDIT: It's also sort of scary to think that it took 4.5 billion years from the first life for us to evolve, and it's only going to be another billion before the growing sun sterilizes the Earth's surface.

This is why whenever I see news like this, I get nervous.