A recent paper in Progress in Biophysics and Molecular Biology, Cause of Cambrian Explosion – Terrestrial or Cosmic?, has caused quite a stir. I think that was the intention, and the majority of journalists ate it up, either not caring if the science was good, or not able to tell.

One main point of the paper is that the Cambrian Explosion – the geologically rapid event about 550 million years ago in which multicellular life appears in the fossil record – was so rapid because it may have been the result of alien genetic information. The authors further argue cephalopods, especially the octopus, are so amazing because they either incorporated alien genes into their makeup, or they are completely alien, coming to earth as cryopreserved eggs inside comets. The third leg of their alleged evidence for panspermia is microfossils found in meteorites.

All three arguments are utter crap. The underlying claim of panspermia – that life has seeded the galaxy from one or a limited number of initial sources – is highly problematic but perhaps not 100% nonsense.

The Three Lines of Evidence

Many science bloggers have trashed this article, doing damage control for the irresponsible journalists who probably should not be covering science stories. I will only quickly summarize here.

The Cambrian Explosion was a dramatic event, on the geologic timescale, but is not something that requires inventing an entirely new hypothesis to explain. It is also not a problem for evolutionary theory, as creationists frequently argue, and as I discuss here. The “explosion” was a period of rapid evolutionary change, but it was not sudden. Current estimates are that the event took place over about 40-50 million years. That is a long time, and long enough for the requisite evolution to occur.

Also, even this is likely an underestimate, resulting from an artifact of the fossil record. What the Cambrian Explosion really documents is the emergence of hard parts that are capable of being fossilized. It’s like turning on a light in a dark room, and then thinking that everything in the room just suddenly materialized.

But if the “hard part” hypothesis is true, then there may be softer fossils that can be found (even if far rarer) that document a longer lead up to the Cambrian. In fact, that is the case. But to be clear, there are phyla that emerge in the Cambrian – it was a period of amazing diversification.

The argument that cephalopods are alien is even more absurd. This is nothing but an argument from personal incredulity (something very familiar to creationists). Cephalopods are an amazing group of animals, very intelligent, with astounding abilities such as the ability to change their color.

It does not, as the authors of this article argue, represent a necessary discontinuity in evolutionary history. Cephalopods appear fully terrestrial, genetically, biochemically, and anatomically. Evolution has produced many “weird” creatures. Further, whenever a small group or even individual species is the sole survivor of a previously larger group, they can look like an outlier. It may prompt questions about how they evolved their extreme anatomy. But when seen in the context of the now extinct larger group, the continuity is more obvious.

Imagine if the humming bird were the only avian survivor. Looked at in isolation, it would seem an impossible creature. As one tiny extension of Avis, however, it is still an amazing group of birds, but does not seem discontinuous with the rest of nature.

The “alien octopus hypothesis” is not only not necessary, it is highly implausible in its own right. The notion that alien DNA or an entire alien creature would fit so seamlessly into Earth biology is absurd. Cephalopods are clearly related to the rest of life on Earth. They do not display alien biochemistry or genetic makeup.

The notion of microfossils in meteorites shows how low the bar of evidence is for the authors, if it can be used to support their underlying panspermia hypothesis. There is no credible evidence of fossils or life in any meteorite. Presented alleged evidence has not been generally accepted by the scientific community, because they are just small bubbles or other features that have much simpler explanations. Seeing single-celled fossils in these structures is a good example of having too active an imagination. At the very least this is not an established line of evidence that can be used to support an even more tenuous hypothesis.

Panspermia

So – this article is not convincing, and essentially cobbles together a host of bad arguments based on flimsy or no evidence. That does not mean that panspermia itself is wrong or not a viable theory. But I do think that the notion of panspermia is on life support.

The idea is that abiogenesis, the origin of life from chemical precursors, is an exceedingly rare event. It may not have happened on Earth at all. Instead, it has occurred somewhere else in the galaxy. Hardly lifeforms then somehow made it off-planet, or survived the death of their host star, locked away in ice, and then seeded the galaxy.

Let’s examine this notion from the two basic broad perspective – evidence and plausibility. The first is easy to summarize – there is zero evidence for panspermia. That is the problem the authors were trying to rectify, entirely unsuccessfully.

Despite their claims, there is no evidence for alien life in meteorites, on the moon, or on Mars. The only point left to argue is, how significant is this lack of evidence? It is a fair point that we haven’t even thoroughly surveyed our own system for life, and so we cannot really say how common life is out there in space. So we might say that while there is currently zero evidence, this isn’t a deal-killer in itself for panspermia. But as I discuss further below – it is a problem.

How plausible is panspermia? This gets to rampant speculation, but let’s do it anyway. Can life survive for millions, even billions, of years as it travels between stars? That seems highly unlikely, and is the most implausible aspect of the hypothesis. We know that DNA does not last for millions of years. Even if cryopreserved, millions of years is a tall order.

Some argue that microscopic life could actually live inside a comet, in pockets, on chemosynthesis. Those would have to be some hardy buggers.

As Caleb A. Scharf pointed out in 2012, this creates a paradox. In order for organisms to be so hardy that they could survive an interstellar trip, they would be capable of living almost anywhere in our solar system. The moon or Mars would be just fine. So why aren’t they everywhere? Why aren’t they in every meteorite?

I would add that if panspermia were true, then why haven’t there been multiple seedings of life throughout the last 4 billions years on Earth? Again, the authors try to solve this problem with their cephalopod argument, but it fails. They are actually just admitting that the problem exists. Life on Earth should be a patchwork, not the seamless tree of life that we see.

Conclusion

In the end, panspermia is an interesting but highly implausible, and entirely unnecessary, hypothesis, with zero supporting evidence.  None of this makes it wrong, but it does relegate it to a fringe hypothesis.

The authors prematurely declare victory for their fringe hypothesis, marshaling terrible arguments and flimsy evidence.