Panspermia
Written by Jean Tate
Instead of life originating here on Earth (abiogenesis), perhaps it came from somewhere else, either in our solar system, or from beyond it? Panspermia is the name for that idea.
Panspermia is a very old idea, dating back to at least the ancient Greeks. Perhaps its most famous, recent, proponents are Fred Hoyle and Chandra Wickramasinghe.
That life could have originated somewhere in our solar system and then spread to Earth is not particularly controversial, today.
For a start, there's pretty good evidence that at least some kinds of bacteria and archaea – and perhaps simple eukaryotes too, a protist for example – could survive a journey between Mars and Earth, inside a rock blasted off by a meteorite impact. After all, there are a number of meteorites, found here on Earth, which came from Mars (and some from the Moon too), and their interplanetary journeys could have been as brief as a century (or less), which lots of prokaryotes could survive in a state of suspended animation (and some species have extremely high radiation tolerance too). While the acceleration of blast-off would likely kill most multicellular organisms, a great many single celled species could survive such a high-g event.
Then there's the overwhelming evidence that conditions on Mars in its early years would have been favorable to life – liquid water, clement temperatures, … More: indirect evidence of life on Earth is as old as the oldest rocks, so perhaps life seeded Earth as soon as the molten oceans solidified (Mars may have had a somewhat more favorable, and stable, environment, for longer, than that of the Hadean Earth).
Less is known about conditions on Venus, the Galilean moons (Io, Europa, Ganymede, Callisto), and Titan – other solar system bodies where life may have begun – during the first ~500 million years or so of their history, so the possibility of any of these seeding life on Earth is more speculative.
The possibility of life originating in other than early-Earth-like environments – such as active iceballs like Enceladus, or comets – is quite speculative, but research over the next decade or three may show it to be quite likely … and the case for panspermia strengthened accordingly.
An interstellar source of seeded life – an older planetary system perhaps – seems quite unlikely, because survival of the seeding life is thought to be zero; the travel times are too long (millions of years), and the possibility of a suitable life-bearing vessel (a cm-sized rock, say) arriving intact in as short a time as 500 million years or so also zero (while a considerable quantity of interstellar grains arrives in the solar system every year, nothing as large as even a sand grain has yet been observed among the arrivals).
Panspermia is popular! Look at all these Universe Today stories on it: Panspermia Flower Power, Life on Ceres: Could the Dwarf Planet be the Root of Panspermia?, An Experiment to Test Panspermia, Did Life Arrive Before the Solar System Even Formed?, If Life Exists on Venus, Could it be Blown to Earth? … and that's just a sample!
Astronomy Cast has a special episode on this topic, Panspermia; well worth a listen.
Filed under: Astronomy
Related stories on Universe Today
- Podcast: Panspermia
- An Experiment to Test Panspermia
- Panspermia Flower Power
- Life on Ceres: Could the Dwarf Planet be the Root of Panspermia?
- Did Life on Earth Originate With Comets?
