Arguments in favor of "Panspermia"

Excerpts from a column at The New Yorker:

I spoke by phone with Gary Ruvkun, a molecular biologist and professor of genetics at Harvard Medical School. Ruvkun has what he admits are somewhat unusual opinions about life’s origins, and about the possibility of finding life elsewhere. In short, he questions the common assumption that our form of DNA-based life began on Earth...

Looking for methane is a good method to indirectly look for life. The problem is, there are chemical ways to make methane as well. It is not a perfect surrogate for life...  My favorite way to look for life is to go to a planet and look for DNA. And that assumes that life on another planet would be exactly like life here, which is not how most astrobiologists think about things...

I find the idea aesthetically appealing that life as we know it is universal across the Milky Way. It just seems like, once it evolves, it spreads... That life didn’t start here. It just landed here. That it came from somewhere else. And a lot of people complain about that. They say, “Well, then you’re just putting the problem of origin of life somewhere else.” Which is true...

See, the thing is, if you look in the fossil record, where’s the first evidence of life? Well, you can see evidence of bacterial life, things that look like bacteria, the things that are called stromatolites, which are a kind of blue-green algae bacteria that live in colonies. Those things form good fossils, and you can see those about three and a half billion years ago... They were super highly evolved, and I think they got here as soon as the Earth cooled, and they just started growing. And they’ve been spreading across the Milky Way and maybe the whole universe...

For background reading - the Wikipedia page on panspermia.

Posted last year: Panspermia and the Cambrian explosion.

And if you wonder about interplanetary transport... This rock found on the moon originated on earth.