Mitochondria carry their own genome, which is substantially different to bacteria. Although nowadays a core part of eukaryotic cells, it's not hard to believe t

Mitochondria carry their own genome, which is substantially different to bacteria. Although nowadays a core part of eukaryotic cells, it's not hard to believe that they were once a separate form of life much simpler than a bacteria. Considering the age of life on this planet, panspermia from Mars is unlikely; in the early life of the solar system, the sun was much dimmer and Mars was significantly colder than today. Any liquid water on the surface, on which life as we know it could have developed, would only be present in fairly recent history (no longer than a billion years really).