Was the asteroid impact that caused the extinction of the dinosaurs a one-off? Or are other mass extinctions in earth’s deep history perhaps also linked to impacts of extraterrestrial bodies? Many scientists are reluctant to accept this idea. In Cataclysms, Rampino argues that it is high time to cast off the spirit of Lyell that continues to haunt geological thinking and embrace a new era of catastrophism.
So, bit of a history lesson first. The British geologist Charles Lyell (1797-1875) published the textbook Principles of Geology that went through 12 editions between 1830 to 1875 and influenced generations of geologists. Three of his ideas became axioms in geology:
1. Geological change is slow and gradual and the result of processes we can see in operation today (to evolutionary biologists like myself this axiom sounds familiar, as Charles Darwin has written the same about evolution. Not strange when you consider Lyell was Darwin’s contemporary and mentor, and heavily influenced his thinking).
2. No need to invoke astronomical influences, geologic forces are intrinsic to the planet.
3. The geologic record does not contain regular patterns influenced by astronomical cycles.
This idea of slow and gradual change is known as uniformitarianism: “the present is the key to the past”. Lyell was firmly opposed to the idea of past catastrophes having influenced the planet, which at the time often took the form of attempts to shoehorn the Biblical flood into the picture (with the exception of Cuvier and some others, who favoured natural explanations). Mind you, Lyell’s ideas are not free from theological underpinnings either. As Rampino shows, close reading of his work clearly shows that a slow unfolding of geological history was God’s plan to shape a world perfectly suited for humans to live in.
Lyell’s views won the day. Discontinuities in the fossil record were explained away with the argument that the geological and fossil record are highly incomplete and fragmentary, like a book from which many pages are missing. So, what seems like species suddenly disappearing is just an illusion, perhaps the result of missing fossils, or of periods of geological strata not being deposited. If the record were complete, it would reveal gradual extinction. There. Done and dusted.
These views continued to dominate geology well into the 20th century, and with that in mind, you can understand how the Alvarez paper, which proposed the dinosaurs were killed by an asteroid impact, caused such a splash. Rampino spends several chapters describing their work, and the subsequent work to gather more supporting evidence. You see, impacts leave tell-tale signs in the geological record due to the extreme forces and temperatures generated upon impact, and Rampino describes these in much more technical detail than The Ends of the World that I read just before this book. Good job that the book is accessibly written, as I was able to follow along just fine during these chapters. Plenty of these signs have been found at the Cretaceous/Paleogene boundary, 65 million years ago, and by now this impact is a widely accepted fact. But was this a one-off? Rampino argues it was not. He describes work by geoscientists who have found signs of impacts at other times in deep history and tries to link these to other (sometimes minor) mass extinctions. For a while I felt a bit sceptical: was he another person who suddenly saw asteroids everywhere? But Rampino is clear-headed enough to admit that not all mass extinctions are impact-related, and highlights the important role of flood basalt eruptions. These episodes of massive catastrophic volcanism were responsible, amongst others, for the end-Permian mass extinction, which wiped out some 95% of species 252 million years ago.
“It’s an interesting idea, and certainly one step up from the Nemesis hypothesis […]”
Even so, it is clear Rampino favours the impact explanation. He points out the incomplete sampling of the geologic record to detect traces of impact, and the difficulties in finding these. Not every asteroid will be a dino-killer. Size, composition, and location of impact will all influence what traces past impacts have left. Add to that that some impact craters, especially older ones, may never be found if they occurred in regions that have since disappeared down the planet’s gullet in subduction zones and have been erased. Clearly, there is a lot more work to be done before we can pin other extinctions on impacts as clearly as has been done for the end-Cretaceous mass extinction. But he thinks that if we look harder, we’ll find more evidence of this.
Rampino goes a step further though – this is where the book gets more controversial – and suggests these impacts occur at roughly 30-million year intervals. These ideas have met with opposition, as many scientists have hypothesised periodic cycles before that have not stood up to scrutiny.
Rampino and co-workers are convinced they are onto something though. They even have a mechanism in mind that, by their own admission, is rather speculative. As our solar system goes around our galaxy (which, as you might know, we have good reason to believe is a disk-shaped spiral galaxy) it oscillates up and down, passing through this disk at intervals of about 30 million years. This would disturb the Oort cloud, a hypothetical band of icy bodies circling the Sun at a great distance, well beyond
Pluto Neptune in interstellar space, sending comets our way. It’s an interesting idea, and certainly one step up from the Nemesis hypothesis, which invoked an as-of-yet undiscovered distant planet as the source of these comets (see The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science for the controversies around that idea).
The really speculative part, which was also recently put forward by Lisa Randall in the book Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe, is the role given to dark matter. Supposedly, above-mentioned disk also houses dark matter, which would add further gravitational pull disturbing the Oort cloud. But wait, there’s more. Some astrophysicists think that dark matter particles could be captured by earth and, once sufficient densities have been reached, could undergo a process of mutual annihilation, producing enormous amounts of heat in the planet’s interior, which would trigger rising plumes of hot material that cause flood basalt eruptions.
“[…] we are at the cusp of a revolution in geological thinking, one that gives more credence to catastrophist explanations, from above and below”
Obviously, these ideas have met with plenty of opposition. Rampino argues that many geologists are still stuck with the heritage of Lyell’s ghost, unwilling to accept any astronomical explanation for geological processes. He thinks we are at the cusp of a revolution in geological thinking, one that gives more credence to catastrophist explanations, from above and below.
I am totally on board with Rampino’s call to abandon Lyell’s uniformitarianism, but almost 40 years after Alvarez’s paper, that’s hardly a revolution anymore, is it? I thought the scientific community is already well on its way to accepting catastrophist explanations. Rampino furthermore outlines some interesting ideas in this book, but until we have gathered more data to support or reject them, they are just that. Speculative ideas. If scientific consensus rolled over at every left-field idea that is presented as the next revolution, we’d be nowhere. So I think the criticism and scepticism levelled at these particular ideas is both necessary and deserved. Luckily, Rampino is enough of a scientist to recognize this himself, which certainly helps his credibility. And Cataclysms is sufficiently well written that I’ll say: “Sure, I’ll entertain your ideas. Let’s see what future research brings.”
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review: