Panspermia is the idea that life could have emerged on an alien planet, and then could have travelled through space to Earth, where it flourished and evolved into all the life we see today. So you, your family and your cat could all be aliens.
In the first post I looked at the idea that this alien life could have been simple bacteria, and could have travelled to Earth early in its history either in spores or in asteroids or comets. This is very much the ‘traditional view’ of panspermia.
In this post I’ll look at some alternative forms of panspermia, such as the idea that intelligent aliens may have deliberately seeded Earth with life.
Our Galaxy, the Milky Way, is extremely old (around 13.2 billion years) and extremely big (with around 300 billion stars). With all this time and space, surely life has emerged many times, and surely on some planets this life has evolved into intelligent civilizations? This is the thinking behind ideas like the Drake equation; that the Earth isn’t special, that many planets with life may exist in the Milky Way. But if this is the case, where are all the aliens? We haven’t found any evidence in space for intelligent alien civilizations – this is called the Fermi paradox (we may have found some evidence for alien Dyson spheres though!)
But maybe there is an answer to the Fermi paradox that many haven’t considered yet. Maybe rather than looking out into space, we should look inwards instead. Proof of intelligent alien civilizations may be found on Earth, inside our own DNA.
The famous Nobel Prize winning biologist Francis Crick (he co-discovered the structure of DNA) and the chemist Leslie Orgel proposed the idea of directed panspermia, that intelligent aliens could deliberately send bacteria to distant planets, in order to spread life throughout the Milky Way. Crick and Orgel believed that life could not have emerged so quickly on Earth, and that unintentional panspermia could occur, but would be very unlikely, so they instead suggested that aliens could deliberately deliver simple life to Earth.
They proposed that aliens could create tough capsules housing a mixture of hardy bacteria, and these could be aimed at the planets of suitable stars and fired as clouds, or placed in spacecraft, to be carried to their new homes. The probability that these capsules would survive the journey and land in suitable locations on suitable planets would be low, but if enough capsules were sent, then life may be able to take-hold in many different locations.
Why intelligent aliens may choose to do this has also been debated and a number of suggestions have been made, including the idea that the Earth could be an alien experiment in the evolution of life, that the alien civilization may be doomed to destruction (perhaps their star is about to go supernova) and they want to ensure that life from their planet, in some form, continues elsewhere in the Milky Way, or even that the aliens have some kind of religious belief that its their duty to spread life throughout the Galaxy. A disturbing idea is that the Earth could have been seeded with life to make it easier for the aliens to colonise, that panspermia was used to terraform the Earth, so that when the aliens arrive it will be habitable for them.
So what about this evidence in our DNA?
Well Crick claimed that the fact that all life on Earth contains such similar DNA was potential proof that it was derived from a reasonably small population of genetically engineered bacteria. He argued that although different organisms have different genomes, the underlying structure of DNA is the same in all life forms. Others have even proposed that DNA may contain hidden clues or codes that have been waiting until an intelligent life form evolved that could read DNA, and could decipher these codes to learn the truth about our extraterrestrial origin.
This DNA evidence sounds fantastic, but unfortunately also sounds like nonsense. Many scientists have argued that the reason all organisms contain similar DNA is that DNA is such a versatile molecule that it may have out-competed alternative forms of genetic code, and that all life on Earth likely evolved from a dominant DNA-based last universal common ancestor, and furthermore, the fact that DNA is so versatile and capable of producing such diverse organisms, means it doesn’t need to be very different.
Perhaps a more likely version of directed panspermia could be called accidental directed panspermia, in which aliens could accidentally seed other planets with life if they transported bacteria to other planets in their spacecraft without realising. If alien explorers were unaware that their craft were carrying bacteria, then each planet they visited could be seeded with life, and on some planets this bacteria could take-hold and create a new biosphere. Life on Earth could have been accidentally seeded by careless aliens, a bit of a let down I know.
This is a concern for human space exploration though. The probes and spacecraft we send to the Moon and the other planets in our Solar System have to be very carefully decontaminated to ensure that we don’t accidentally transport bacteria from Earth into space. In the first post I even gave a possible example of this, with the lander Surveyor 3 potentially accidentally carrying a bacteria called Streptococcus mitis to the Moon in 1967. This may not be such a problem on the Moon or Mars, where bacteria is unlikely to be able to survive for long, but if we send probes to explore the predicted oceans under the surface of Europa and Callisto, then these oceans could support life, and bacteria accidentally transported from Earth could survive in these oceans, and may threaten any life that already exists there.
An even more extreme version of directed panspermia has been proposed by Erich Von Däniken in his books, such as Chariots of the Gods, he claimed that an ancient alien civilization came to Earth in the past and gave humanity the knowledge and technologies to create our civilization, such as language, writing, farming and construction techniques. He even proposed that the evolution of humans might have been shaped and directed by aliens. Von Däniken claims the evidence is abundant, in cave paintings, in ancient constructions such as Stonehenge and the pyramids in Egypt and Mesoamerican, and in religious and historic writing, such as the angels from the Bible and the myth of Atlantis. Anyone who’s a fan of Stargate will find all this pretty familiar.
Von Däniken’s ideas are great fun, and have made him rich and famous, but the evidence does not stand up to serious investigation. It’s a great story, but nothing more.
I think the same is true of directed panspermia, whether intentional or accidental. In the first post I wrote that “extraordinary claims require extraordinary evidence”. This was a quote from Carl Sagan; he said that if you have extreme scientific ideas, then you really need to have some strong evidence to back them up. Directed panspermia doesn’t have any of this evidence. These ideas are possible and could be true, but they probably aren’t. Life probably emerged and evolved on Earth through chemical evolution, without interference from alien life.
But if bacteria didn’t arrive from the stars, and life did emerge on Earth via chemical evolution, a less extreme form of panspermia could still be involved.
In September 1969 a sonic boom ripped through the sky over Melbourne in Australia, as a meteorite crashed to Earth. The meteorite is known as the Murchison meteorite and was found to be a carbonaceous chondrite, a type of meteorite rich in carbon. Upon analysis it was soon discovered that Murchison contained a range of biological molecules, including amino acids, sugars, DNA bases and fat molecules that must have been created in space. Murchison raised the idea that simple organic molecules could be created in space by natural processes, that our Galaxy may be rich in organic molecules spread throughout space. Since this initial discovery, similar organic molecules have been found in other locations in space, including within asteroids and comets, providing more evidence for this idea.
This had led a number of scientists to propose that organic molecules could have been manufactured in space as our Solar System formed, and then could have been delivered to the early Earth in asteroids, and particularly comets, which could have delivered both large amounts of water and biological molecules. Living cells may not have been delivered to Earth from space, as in the traditional view of panspermia, but extraterrestrial biological molecules could have been, and could have then undergone chemical evolution to create the first life on Earth.
I believe that most versions of panspermia are unlikely, but that this last version could be close to the truth. We don’t know exactly when life emerged on Earth, but the evidence we have suggests it may have happened reasonably quickly, almost as soon as it was possible, likely between 3.5 to 3.85 billion years ago. However, around 3.9 billion years ago the inner Solar System went through a period of intense bombardment from asteroids and comets called the Late Heavy Bombardment Period, that would likely have made Earth inhospitable. Yet life appears to have emerged soon after this period. Could the Late Heavy Bombardment have delivered the building blocks of life to Earth?
Next I’ll look at a recent claim that fossilized life has been found in a meteorite, and in the last post I’ll look at some cool panspermia ideas from sci-fi films, TV and books.