>UNLESS, Panspermia is correct and all life on earth came from space, in which case it would be completely in the realm of possibility that life from space that

>UNLESS, Panspermia is correct and all life on earth came from space, in which case it would be completely in the realm of possibility that life from space that landed on earth had already landed here before, in the distance past. The earliest known life on earth is cyanobacteria from 3.5 billion years ago. The earliest diatoms we've found are from 185 million years ago, and they are believed to have arisen around 250 million years ago. So even assuming that the earliest life on Earth included diatoms, that leaves over 3 billion years between the earliest specimens observed and these hypothetically original specimens. I don't think the odds are even worth considering that a species adapted for an extraterrestrial environment would be visually recognizable after 3 billion years of terrestrial evolution.