Panspermia is an old idea that life arrived on earth from outer space, by a meteor, landing in the oceans, carrying some bacteria or other ancient life form.
This theory relieves the extremely tight time constraint that otherwise would be given for DNA-based life forms to develop on Earth, after the formation of Oceans - which is estimated like 200-400 million years.
But I would propose another way how abiogenesis could occur in the vast universe, and appear on Earth as a result of trial-and-error on billions of other planets: I believe that abiogenesis and evolution is actually occurring concurrently on an infinite number of earth-like planets, failing on most of them, - but we can observe it only on those planets where intelligent life forms, like humans have developed.
Unlike with panspermia, my theory does not need the germs to travel from one solar system to another, - actually, it can well be that the nearest planet with DNA-based life would be far beyond the boundary of the observable Universe.
This is the Table of Contents for my theory:
The actual shape and size of the Universe is not well understood by laymen, and many people think that the universe is boundless, but finite, like a 4-dimensional sphere. And indeed, this is a valid solution of Einstein’s field equation.
But a completely flat, infinite space is also a solution, and recent experimental data on microwave background radiaton supports this notion.
Which means there are infinitely many galaxies, like ours, in the universe, and infinitely many Earth-like planets.
This notion changes everything for evolution and abiogenesis.
By way do we need a theory? What’s wrong with the current theory? It is the idea of blind search, driven by ‘survival of the fittest’, or ‘natural selection’, which might not have the computational power to produce some of the complexities that we observe.
As natural selection is replaced by anthropic selection, the mechanism of speciation: mutations, genetic drift, and fixation / loss, is also replaced by a novel mechanism: speciation by genomic bistability. In short, noncoding genomic regions accumulate mutations until a tipping point is reached and the gene boundaries are reorganized.
A difficulty of my theory is how to explain ’sidebranch complexity: as it would be expected that anthropic selection prefers earth-like planets with very low biodiversity, the tree-of-life practically reduced to a single, very tall, barren shaft. But that’s misconception that stems from assuming probability of outcomes that cannot be measured.