On this blog, I’ve often mentioned the tendency and the temptation to look at the past as if it’s just a prologue to the present. If that’s so, that would surely make the present a prologue to the future, which seems silly. In fact the past was the way the present used to be and we should appreciate the past in all its pastness. I sometimes joke that all the years after 1984 CE are just made up, because that year seems to be the peak of my reminiscence bump.
Consider, then, the above image. I can’t say I’m fully aware of every species of animal in it but I suspect that some of them are only included because they’re close to the ancestors of species we’re familiar with today. For instance, I spy tiny horses, but back in the day Hyracotherium wasn’t a tiny horse waiting for the grasslands to develop so she could get bigger and gallop across them as some kind of vaguely hare-like animal living in the leafy undergrowth of the rainforests, even though their children’s children’s children’s . . . children would be horses, zebras and donkeys.
The above scene is from the Eocene. This used to be thought of as happening immediately after the Chicxulub Impactor led to the deaths of all but the smallest dinosaurs, but nowadays the Palæocene has been inserted between that incident and the start of the Eocene, so it’s now seen as starting later than it used to be and doesn’t have the specialness of being immediately after the big kablooie. Because of the older idea that the dinosaurs (who used to be decidedly non-birdy) were cold-blooded and had died out because of climate change, i.e. it got too cold for them and they all died of hypothermia or something, I used to think of the Eocene as kind of cold and rainy. After all, if “warm-blooded” animals like mammals and birds were able to thrive during it and the dinosaurs, being cold-blooded, couldn’t, it seems to make sense that it was not very warm.
In fact, the opposite is the case. The Eocene was ludicrously and stupendously warm. It was so warm that there were tropial rainforests in the Arctic and the polar ocean was like a warm bath in temperature. It was hotter than the age of dinosaurs by far, and even in 24-hour darkness it stayed warm enough for there to be hot, steamy jungles. I find this utterly confounding, because in such conditions mammals would seem to be at a disadvantage compared to reptiles. They’d be expending loads of energy just trying to keep themselves cool enough not to succumb to heatstroke. Then again, maybe this is the answer. The reptiles maybe didn’t do so well because they were heated by the ambient temperature, whereas mammals were better at keeping their temperatures lower. Maybe the truth about mammals is that far from being warm-blooded, they were actually cold-blooded, in that they were kind of living self-refrigerators, and it was this which enabled them to survive such a sultry planet. But it still doesn’t make much sense to me, particularly because the lack of daylight which went on for months at a time at the poles still didn’t make it cold.
That, then, is one major odd thing about the Eocene, but it isn’t alone and it isn’t the only weirdness. The fact is that of all suspect times in the planet’s history, the Eocene is the best fit for the Silurian Hypothesis. If you just want a breakdown of that in general, feel free to follow the link, but the basic idea is that because we have quite good evidence for how our own civilisation is affecting the planet, we can look back into the past and find other times in the geological record where something similar happened, and perhaps conjecture that the reason it did so was that there was an advanced civilisation on Earth at the time. There are a number of candidates for this idea, but by far the best in terms of several different technosignatures coinciding takes place during the Eocene.
A technosignature is a sign, perhaps observable from another star system, that advanced technology is or has been in use on a particular planet or in a particular star system. It might be something like a planet with fluorine compounds in its atmosphere or an unusually high level of carbon dioxide as well as oxygen. I’ve just made those up by the way. At the moment, something a little suspicious has been noticed in stars near Tabby’s Star which may be along these lines. Tabby’s Star is a star with an unusual pattern of dimming which it was tentatively suggested might be evidence for a megastructure such as a Dyson Swarm around it. Simpler and better explanations have been offered for that individual star, involving dust and unusual but feasible patterns of comets, but it’s more recently been found that the pattern is found in stars near Tabby’s Star itself which are exactly the types of star expected to be suitable for life. Although it’s strongly tempting to imagine an interstellar civilisation based on this, this can amount to “a wizard did it”, i.e. it’s the go-to explanation for anything unexplained, and it’s not boring enough to be true.
The Silurian Hypothesis is named after the ‘Doctor Who’ monsters known as the Silurians. Perhaps coincidentally, these don’t date from the Silurian itself, although the name sounds cooler, but from the Eocene. They hibernate for millions of years before emerging from their slumber to find the mammals have taken over, so they actually belong here and are not aliens, but as befits the pulpy nature of Who, which it’s no worse for, this is all a bit thrown together like that bit in ‘City Of Death’ where life is supposed to have begun 300 million years ago rather than over ten times further back than that. But I can forgive that because it’s by Douglas Adams. The Silurian Period itself was before vertebrates had heaved themselves out of the water, or rather found themselves in increasingly shallow deoxygenated water until they were just squelching about in mud, so it doesn’t seem to lend itself that well to a race worthy of the name, but is actually named after a Pre-Roman Celtic tribe native to what has become Southeast Wales. It also happens to be found in the zoölogical name for catfish, the siluriformes, and the idea of vaguely vertebrate-looking aliens with tentacles on their faces instead of hands is quite appealingly exotic and perhaps creepy, but Doctor Who Silurians don’t look like that at all.
This subject is kind of about aliens, but in another way it isn’t. However, the circumstances of the Eocene suggest that if something did happen then it wouldn’t have originated from this planet, because it doesn’t look very promising. The non-avian dinosaurs, which had reached some kind of climax, had just been wiped out (fifteen million years is not necessarily a long time geologically) but the placental mammals hadn’t had time to get very far yet. The Eocene placental mammals were very diverse, because evolution had enabled them to radiate into the newly vacated ecological niches very fast, but there would later be a reckoning leading to most of those groups becoming extinct. Therefore it doesn’t seem very likely a technological civilisation would appear among them.
It should also be borne in mind that the Eocene is a long stretch of time compared to human history, from 56 to 33.9 million years ago or more than twenty-two million years. Taking the persistence of behavioural modernity as the starting point of our history (the likes of cosmetics, jewellery, cave art, burial customs and so forth), five hundred centuries ago, this is over four hundred times as long. Thus the geological record of a prehistoric civilisation would be quite short and abrupt.
I don’t want to repeat what I said in the original article here because my focus is a bit different, but for convenience’s sake, what we will leave in the geological record is a mark of the damage, though temporary, we’re doing to the environment and there are a number of possibilities. Firstly, light elements cycling through the biosphere and other cycles without technological intervention have a distinctive isotopic profile because they’re exposed to solar radiation and this changes the number of neutrons in their atoms, whereas the same elements buried deep underground are shielded from this by layers of rock which block the same radiation. Hence the nitrogen in fertilisers which has been mined rather than, for instance, being derived from guano as is traditional has different proportions of isotopes in it. The carbon implicated in anthropogenic climate change is also different because it was taken from coal and oil. Although many isotopes are unstable and will have disappeared from the record in millions of years, some are stable and will be preserved. There are also transuranic elements which are relatively stable, such as isotopes of plutonium and curium, whose half-lives are in the millions of years. Curium in particular doesn’t occur in any significant quantities on planets. Increased soil erosion also results in faster rates of sedimentation in rivers and estuaries, associated in part with the greater use of nitrogen fertilisers, and there are dead zones in the oceans as a result of nitrogen in this form allowing microörganism growth to outstrip the supply of oxygen. This can be seen to show up in the geological record, for instance at the biggest extinction of all at the end of the Permian, so it clearly does leave a mark. Incidentally, some scientists believe this is the main direct cause of mass extinctions. There are more rats and mice around than before, so an increase in the occurrence of particular fossils might be another sign. Technology is also able to create compounds more stable than those which arise without intervention, such as ones where chlorine and carbon are bonded, hexafluoroethane and sulphur hexafluoride, which will persist in the environment for hundreds of millions of years if not longer. Organic compounds formed biologically also have handedness, although in the case of amino acids these become mixtures over thousands of years, so the presence of steroids in mixtures of left- and right-handed forms, for example, would be a good sign. And of course there are plastics, although some of these are stimulating the evolution of bacteria which can digest them, or the proliferation of long-existing organisms who already could.
Ocean anoxia has occurred quite often in terms of the geological timescale of events. The aforementioned incident at the end of the Permian is one example. Others are seven such events, three of which were localised and minor, in the Cretaceous, and one in the Jurassic, often associated with an increase in carbon-13. There also seems to have been greater ocean sedimentation during these occurrences. There was also such an event in the Devonian, and particularly reminiscent of our time of deforestation, the loss of the Carboniferous rainforests is quite a 21st century event for so long ago.
But for some reason the Eocene has a cluster of such markers. The start of the Eocene 56 million years ago is officially marked by a sudden increase in the carbon and oxygen isotopes which in our time mark civilisation. For between one hundred and two hundred millennia, stable isotopes of carbon and oxygen other than the most common types both became more common. There was also global warming up to 7°C at the time. Vanadium, zinc, chromium and molybdenum all increased while this was going on, as did sedimentation in the oceans. Over the six million years after this, there were four more such events, although less dramatic, then forty million years ago there’s one more. The interesting thing about these is that the combination of unusual isotopes, global warming, apparent soil erosion and metals used in industrial processes all occur together, just as they are today.
One good argument against the existence of aliens is that we’re here at all. It seems that if a technology like ours arrived here in the æons of time over which life has existed on this planet, it would’ve caused serious damage to Earth’s ecosystem and perhaps wiped out all complex life, but there are no such incidents in our history. There’s also no species which isn’t related to all others, as might be expected if alien microbes had arrived on this planet later than the possibly first alien microbes to whom we might all be related. Hence we have to confront the rather disturbing prospect of a friendly habitable planet (at least to us) sitting here for countless millions of years without one single alien spacecraft landing on it, and that suggests there are no aliens, or at least no aliens yet. However, if there are recurring incidents of this kind in the geological record, the quandary becomes somewhat different, because instead of Earth never having been visited, the issue becomes the absence of alien microbes or other life forms on this planet. That issue, however, could be circumvented if it turns out these civilisations, which may of course never have happened, are actually from here, but the problem is then what animals they evolved from. The Palæocene is if anything even less promising than the later Eocene in this respect.
There are, then, three possibilities:
- There has never been an advanced technological civilisation on this planet and the apparent technosignatures are just coincidences explained by other processes. This, being the most boring possibility, is the most plausible by far.
- There has been at least one advanced technological civilisation which evolved from organisms already living here.
- The planet has been visited and settled by advanced aliens.
- There is a mixture of native and alien civilisations through our geological history.
The events of the Cretaceous may be more compatible with the idea of intelligent dinosaurs. The run up to the Cretaceous is many millions of years long, giving dinosaurs with human-like intelligence a lot of time to evolve, and some of the dinosaurs living today, such as parrots and crows, manage to achieve intelligence very similar to ours in spite of brains only weighing about thirty grammes compared to our fifteen hundred. However, the Eocene is more puzzling. The recent impact which had wiped out the larger dinosaurs did stimulate evolution, as mass extinctions often do, but it also caused the extinction of all larger animals, which are able to have larger brains, and it seems like it would’ve taken a long time for them to get that brain power back.
As a child, I made the following conjectures about past technological species here:
- At the end of the Permian period, a species of mammaliforms evolved human-like intelligence and founded a civilisation which had such a devastating effect on the planet that it caused a mass extinction.
- The coleurosaur (bipedal dinosaur with binocular vision and opposable thumbs – or at least I thought so at the time) Saurornithoides established a civilisation and wiped themselves out in a nuclear war, thereby explaining the iridium anomaly.
- The ancestors of dolphins had their own technological culture about twenty-five million years ago, which is the point when their brains reached ours in size.
- Homo erectus achieved an interstellar civilisation 800 000 years ago which only collapsed at the end of the last Ice Age.
I no longer believe in any of this, but I would want to modify the dinosaur one in particular, which I think is by far the most feasible, to incorporate Chicxulub, in that they could have moved an iridium-rich asteroid into orbit around this planet as a source of metals and accidentally crashed it into the Gulf of Mexico. The Cenozoic ones don’t line up with the events in the Eocene. Homo erectus evolved in the Pleistocene and the dolphins reached that stage in the late Oligocene, eight million years after the end of the Eocene.
The trouble with all of this is that it has a kind of quirky, eccentric sound to it and seems to be way outside of the scientific establishment. It’s particularly similar to tales of Atlantis and Von Däniken’s ancient astronauts, whichever version of the hypothesis you go with, apart from the first of course. On the other hand, why should we be the first, either in the whole Galaxy or on this planet? It seems arrogant to assume that, and on the whole we’re supposed to go with the Copernican Principle that there’s nothing special about us, and if there isn’t, maybe we aren’t the first, even on Earth. However, if there was a civilisation here during the Eocene, it seems unlikely it was from here, so maybe back then Earth was an outpost of the Pwqu Empire or something. After all, they left that giant mouth thing on that planet didn’t they?
Could it actually be Earth that was the cradle of interstellar civilisations at this time? There are reasons to suppose not. This would be the inverse of the possibility that aliens have visited this planet, because the chances are they would’ve left genetic traces as unrelated organisms. If the Galaxy had been filled by countless Earth colonies back in the Eocene, we’d be more likely to be living on one and find that there were two strains of life on it rather than the single one we observed. On the other hand, it is a bit odd that the first organisms on this planet seem to have been here during the Hadean, before Earth had even become even slightly habitable, so is it possible that all life in the Universe, or perhaps locally, is related and we’re looking at an extraterrestrial rather than a terrestrial common ancestor?
The kind of civilisation we’re looking for here is very much modelled after our own post-industrial, science-dominated culture, and it doesn’t follow that those would be the kind of societies which emerged millions of years ago. For all we know, and that phrase takes the proposition out of science because there’s no evidence but it’s still rational, civilisations may have evolved which were either very advanced in other ways or more cautious and reverent of Mother Nature. Maybe we don’t see evidence of civilisations like ours because we’re an anomaly, not because we are a community of sentient beings using technology but because of what we’ve done with it, or maybe other civilisations too went through an unsustainable industrial phase but ended up cleaning up after themselves. Nonetheless there is limited evidence for a civilisation in the Eocene, or perhaps a whole cycle of civilisations over millions of years, maybe collapsing due to unsustainability and environmental catastrophe before slowly making their way up the ladder, only to fall again millions of years later.
This may actually give us some hope. If the influence of past civilisations is so difficult for us to detect today that even the most recent ones, forty million years ago, managed to poo in its own bed so seriously that it wiped itself out and the planet recovered so well we can’t even tell it was there nowadays, it suggests that Earth has very powerful capacity to heal itself, and has done so before from the very onslaught we’re committing today. However, there’s no longer any trace of any putative civilisation remaining, which is also food for thought. We could, geologically speaking, be so thoroughly gone that nobody will ever even know we existed.
A Box Of Chocolates 