Abiogenesis is the process by which nonliving matter turns into living matter—that is, something that natural selection can work with. This is thought to be how life on earth originated, though there is no consensus on how this happened. Evolution then shaped that early life into what we see today.
But there is another hypothesis.
Asteroids that hit the earth are mostly bits of rock that formed from the early accretions of and collisions with material in the early solar system. Sometimes, however, big asteroid impacts can eject material from a planet, and this new material itself can become asteroids. If this planet had life, the new asteroids might be contaminated with bacteria that, if they fell on another planet with the right conditions, could seed an otherwise barren planet with life.
This is the idea behind panspermia. It bypasses the problem of a planet having the right conditions for sustaining life but not the right conditions for creating it.
A variation is directed panspermia, the idea of panspermia being not accidental but deliberate. Imagine an advanced civilization deliberately sending out durable primitive life on rocks or satellites to infect sterile planets.
But does panspermia simply move the problem rather than solving it? The buck has to stop somewhere; how does panspermia help?
This was the reaction by some Creationists to Richard Dawkins’ interview with Ben Stein for the movie Expelled (video, go to 4:00). Dawkins was caricatured as saying, “How do we explain how life started on earth? Imagine that it was put here by aliens. Problem solved!”
The early earth had a certain set of initial conditions—amount of water, a particular gas mixture in the atmosphere, available chemicals, temperature, range of salinity and alkalinity, amount of sunshine, and so on. What if those initial conditions could never allow abiogenesis but the different conditions on another planet could? Panspermia is the mechanism in which the otherwise-barren planet could be seeded with life. Panspermia in effect expands the initial conditions.
Of course, that may not please the Creationists as much as the caricature, but that’s the lot of science.
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- See all the definitions in the Cross Examined Glossary.