[ Who’s to say the ‘microbes’ aren’t from Earth? 65 million years ago, give or take a million or so, a huge something hit the Earth. It could have thrown up tons of dust and rock into space that drifted through space another million years or two or three or four, then finally came to rest on Mars, carrying ‘life’ from here................... ]
Nice Yarn.. I like mine...
Since ‘man’ has only been in existence as a species for a couple of million years, lots stuff can happen.......
A few close fly bys here and there, maybe a bump or two.
Sharing atmospheres or a few tons of matter here and there isn't too far fetched.