Panspermia sounds like science fiction, but it is a serious scientific theory that seeks to examine if life on Earth arose from outer space.

According to the Oxford dictionary:

  • Panspermia is the theory that life on the earth originated from micro-organisms or chemical precursors of life present in outer space and able to initiate life on reaching a suitable environment.

There are three possibilities when it comes to panspermia

  1. Life arose on Earth independent of any influence from space
  2. The building blocks of life arrived from space
  3. Life arrived from space

Let’s examine each of these possibilities

Life arose on Earth independent of any influence from space


Artist’s impression of a baby star still surrounded by a protoplanetary disc

Credit: ESO/L. Calçada

This first possibility is pretty quickly dismissed by everyone other than creationists.

Earth is not special in a cosmological sense. Earth is not a separate entity somehow set apart from the universe, it is a miniscule part of the universe.

Earth is comprised of debris from space, having been formed as part of the accretion disk that swirled around a newly born star we’ve conveniently named the Sun.

The Sun (and consequently Earth) are second-generation celestial objects. Apart from hydrogen and possibly some trace parts of helium and lithium formed in the Big Bang, every other atom in every single molecule on Earth originated in the fiery heart of a previous generation of stars.

Life arose on a planet that was the result of natural processes in the depths of space, so in some way, panspermia played a part.

The building blocks of life arrived from space

Comet Hits New York City

Comet Hits New York City

Credit: Sandia National Laboratories

The use of the term “precursor” in the definition of panspermia makes the concept quite broad. In other words, Earth need not be “seeded with life” (either deliberately or via happenstance), it could simply be that the emergence of life was facilitated by the arrival of celestial ingredients on comets and meteorites.

This might sound far fetched at first, but it’s actually quite plausible when you consider that during the Late Heavy Bombardment our planet was inundated with…

  • 20,000+ impacts leaving craters over 12 miles in diameter (20 km)
  • 40 impacts leaving craters 600 miles wide (1000km)
  • several basins over 3000 miles wide (5000km+)

Earth’s oceans, as an example, probably originated from water-bearing asteroids arriving during this period.

There are vast clouds of pre-organic molecules in absurd abundance in space. Glycine – CH2NH2COOH – is the simplest of the 20 amino acids that make up our bodies, and it can be found in mind-bogglingly huge molecular clouds in Sagittarius B2 (spanning 150 light years) and the Orion nebula (spanning 24 light years and estimated to contain 2000 times the mass of our Sun).

We know of comets that have originated from outside our solar system, meaning they’re not comprised of the material that coalesced into the Sun and planets, raising the possibility of trans-stellar panspermia from molecular clouds such as those we see in Sagittarius and Orion.

In addition to this, comets need not have deposited life or even the building blocks of life on Earth, as research has revealed that the intense pressures and temperatures that occur during an impact can give rise to the building blocks of RNA.

…models predicted that an oblique impact could give rise to nitrogen-containing hydrocarbon rings, the major structural component of RNA’s nitrogenous bases… more violent collisions could power the creation of long-chain carbon molecules like those that form the backbone of many amino acids…

Experiments have also shown that the conditions experienced in deep space allow for the natural formation “dipeptides – linked pairs of amino acids.” Space, it seems, is a veritable play-pit full of the Lego blocks required to build life.

During the Late Heavy Bombardment, upwards of a hundred million tons of precursor material arrived every year!

Life arrived from space

Tardigrades survived for 10 days unprotected in space

Tardigrades survived for 10 days unprotected in space

Credit: Getty Images

We know life can survive in space. Micro-animals such as Tardigrades (water bears) have been revived after spending ten days in the vacuum of space, while lichen has survived for 18 months on the outside of the space station.

As impressive as this seems, life would have to survive for millions to hundreds of millions of years for panspermia to directly seed life on Earth, making this form of panspermia highly unlikely but not strictly impossible.

An experiment at the University of Kent has shown a small percentage of algae can survive an impact at 6.93 kilometers per second, so life could arrive on the back of a cataclysmic comet impact.

Scanning electron microscope image of the diatom frustule

Scanning electron microscope image of the diatom frustule

Just last week, researchers at the University of Sheffield announced they’d collected atmospheric samples from the stratosphere above England. To their surprise, they found the damaged remains of what looks remarkably like a diatom, a form of algae.

Because such particles have no known way of reaching this height and can only stay aloft for a few hours, they speculate that these diatoms have come from comet or meteorite dust.

As anywhere from 3 to 100 tons of cosmic dust enters the atmosphere every day, this is plausible, but there could easily be some other mechanism at work circulating diatom fragments that we aren’t aware of yet, making this a terrestrial contaminant.

Skeptics have suggested the diatom is far more likely to be a contaminant from the balloon or from lower in the atmosphere, picked up as the balloon rose. As diatoms such as this one are thought to be a recent evolutionary development (ie, within the last 250 million years), it is not likely this is a sample of extraterrestrial life that’s been drifting around frozen for billions of years.

The experiment needs to be independently repeated, as if this controversial finding is correct, then Earth is being continually “seeded” and has been for billions of years. Although this seems extraordinary, it wouldn’t be the first time science has turned out to be stranger than science fiction, but the mostly likely outcome is that this is a false positive.

To put this experiment in context, the collection was conducted at 22-27 km above Earth’s surface (70,000 to 88,000 ft). Commercial airliners fly at roughly 9 km or 30,000 ft, so repeating this experiment in a controlled manner won’t be easy.

The following image is of a high-altitude balloon bursting at roughly 33 km, giving you a good idea of just how far up this collection occurred.


High-altitude balloon bursts at 33km

Credit: Slaros project

Panspermia is a fascinating concept, and one that continues to gather more interest and more research.

4 thoughts on “Panspermia

  1. I think all three possibilities, and a little more besides, would account for the vast varieties of life on Earth…
    and that tardigrade looks like an ant wearing a Halloween costume. See all the folds there… 🙂
    Fascinating article as always.

  2. That first scene in Prometheus gets my vote. That would be possibility 4: Otherworldly engineers Intentionally brought life to Earth solely to baffle members of the intelligent species that would eventually rise to dominance.

    • You’re baiting me… and it’s working… ha ha… Thing is, if there had been Erich Von Daniken style alien engineers tampering with our genes we’d see it in the phylogenetic record (which in many ways is better than the fossil record). Rather than slow, steady branching adaptations, we’d see a stark break where “new code” was introduced.

      Actually, that’s a strike against #3 as well, as if Earth was seeded with anything other than the most primitive and archaic of organisms, we’d see that as a break/disruption in our branching genetic tree. And conversely, if Earth was continually seeded with the most primitive and archaic organisms from space, we’d see evidence of that as well (multiple starting points at different times in different locations). Life is predatory, so latecomers wouldn’t be welcome, but given what we know of how microbes swap organisms we’d see some imprint on the genetic record. What we see is slowly branching diversity that is in harmony with Natural Selection.

      My money’s on #2 🙂

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