For half the history of life on Earth there were no multicellular animals at all[1]. Given how quickly life on Earth arrived I wouldn't be surprised if there w

For half the history of life on Earth there were no multicellular animals at all[1]. Given how quickly life on Earth arrived I wouldn't be surprised if there were bacteria on Mars. But given how long it took Earth life to develop Eukaryotic cells I'd be surprised if Mars ever developed something as sophisticated as an amoeba. Still, Bacteria do leave fossils like stromatolites and some scientists even think some Mars rock parts look sort of like bacteria fossils[2]. But those are more ambiguous than little skeletons or shells. [1]https://en.wikipedia.org/wiki/History_of_Earth https://en.wikipedia.org/wiki/History_of_Earth [2]https://en.wikipedia.org/wiki/Allan_Hills_84001#:~:text=In%201996%2C%20a%20group%20of,speech%20about%20the%20potential%20discovery https://en.wikipedia.org/wiki/Allan_Hills_84001#:~:text=In%2....