I've long suspected that there are parts of the Hoyle-Wickramasingh Hypothesis that are more likely correct than not.
OK, WTF is the Hoyle-Whatchamacallit Hypothesis? (Which I'll call the HWH for short).
Basically, look at the conditions on Earth when Life-as-we-know-it is believed to have formed. Water available, Carbon available, unfiltered sunlight available, and a clay or other substrate (floor) with regularities that would encourage formation of complex compounds.
The take a look at the conditions in the Oort cloud, in insterstellar gas clouds, and in infalling comets. A few quick mathematical calculations will show that theres heaps, piles, zillions more places where conditions like this exist in Space than on a planet's surface. The difference between a few flecks of paint on the surface of some very small marbles, and great vats of paint the size of Jupiter. Now whether the difference is mere Billions or Trillions or something much greater really doesn't matter, the weak form of the HWH says that Life more probably evolved "out there" than "down here". The strong form states that we're constantly being bombarded with biochemical material from space, and that there's a correlation between Viral outbreaks and patterns of infall.
I'm not convinced of the latter. The "fossil bacteria" found in some meteors may be exactly that, or they may be unusual non-living crystal growths.
On the other hand, we know from Surveyor 3 that some common earthly bacteria are hardy brutes, capable of surving in space for some years. Though there is some evidence that the initial reports may have been the result of cross-contamination.
But there's another form of cross-contamination: Martian meteors have been found in Antarctica. (Why Antarctica? Because that's the best place they'd be preserved intact. Dark objects on White backgrounds are easy to find, too)
And now it appears that we've found the other part of the puzzle : similar material on Mars.
NASA's Opportunity rover has examined an odd volcanic rock on the plains of Mars' Meridiani Planum region with a composition unlike anything seen on Mars before, but scientists have found similarities to meteorites that fell to Earth.We haven't found Earth-formed rock on Mars yet, but the evidence indicates there's been an exchange of material between the Earth and Mars - and a pretty hefty one, otherwise the odds of finding such a rock so quickly would be, er, astronomical. (Sorry).
"We think we have a rock similar to something found on Earth," said Dr. Benton Clark of Lockheed Martin Space Systems, Denver, science-team member for the Opportunity and Spirit rovers on Mars.
That means there's likely been a lesser exchange with every planetary body in the Solar System- including Europa.
Put all the clues together, and they indicate that Life-as-we-know-it, carbon-based, water-soluble life, could be incredibly prolific throughout the Universe. Absolutely everywhere it can exist, in fact. And Cross-Contamination means that every bit will have startling resemblances to every other bit, say as much as Botulinum Bacteria does to Elephants, or Tobacco Mozaic Virus does to Goldfish. (Which is quite a lot, from a biochemical viewpoint).