Incoming! Or, why we should stop worrying and learn to love the meteorite
TED NIELD Published by: GRANTA BOOKS Publication Date: January 2011. ISBN: 9781847082640 (pbk) £9.99 ISBN: 9781847082411 (hbk) £20.00
Meteorites have had bad press in recent years. Small ones, that burn up spectacularly as they enter Earth's atmosphere producing a romantic shooting star - fine. Meteorites the size of footballs that hurtle rumbling and sparking to Earth, hitting the odd person – well for them maybe not quite so fine. But the big ones, the really big ones the size of Basingstoke that hurtle through the atmosphere at 30km a second can be very bad for your health - especially if you were a dinosaur. Or so the story goes.
We have had a love/hate relationship with stars, be they fixed or shooting, for an inordinately long time. They have either been praised (presumably to the heavens) or else blamed for their positive or iniquitous influences on the mortal affairs of man. Michael Drayton put it this way in his Endimion and Phoebe (1595):
And by their influence powerfull on the earth,
Predominant in mans fraile mortall bearth,
And that our lives effects and fortunes are,
As is that happy or unlucky Starre,
Which reigning in our frayle nativitie
Seales up the secrets of our destinie,
With friendly Plannets in conjunction set,
Or els with other meerely opposet.
The stars had their good side and their bad. They could either smile benignly or spit malevolence on all in society, affecting the fortunes of kings as they did the fortunes of peasants. When they looked kindly on the populace and were the bestowers of beneficence they were ‘blessed stars’ or ‘lucky stars’. But life is all too rarely a bed of roses, and the speckled firmament takes its fair share of the blame - stars could be malevolent, malicious, wrathful and oppressive, and perhaps even the cause of pestilence. Furthermore, some stars have the rather unnerving habit of just falling from the sky. And there are those who think that, for some creatures, this could have been a very bad thing indeed.
Sixty-five million years ago a disaster struck the world of dinosaurs and of the beautiful, coiled marine shells called ammonites. After diversifying for about 150 million years, these animals vanished from the face of the Earth, seemingly overnight (geologically speaking). The culprit, it has been said, was a rather large lump of celestial rock. Somewhat appropriately the word ‘disaster’, which has its root in the Latin word ‘aster’, meaning ‘star’, derives from the Old French word ‘desastre’ meaning ‘evil star’ – something that goes against the stars, against our destiny. The idea is that if our destiny is linked to the stars, then an evil star will cause misfortune to our destiny.
As Ted Nield points out in Incoming, it took unto the end of the 18th Century for the ‘savants’ to accept the fact that, strange as it might seem, rocks can fall out of the sky. Peasants had been observing it for thousands of years. But what would they know? With the publication in 1794 of his small, 63 page book, Ernst Florens Friedrich Chladni, the physician, musician and inventor (he invented the glass harmonica, giving Mozart the opportunity of composing something for a really strange instrument), contradicted all the scientific wisdom of the time by pointing out that the peasants actually knew what they were talking about. Meteoritic stones did indeed fall from the heavens, hurtling through the atmosphere as a burning fireball. And Chladni was spectacularly vindicated eight years later.
The same Dr Jekyll and Mr Hyde characteristics ascribed to stars can also be ascribed to the gods who had been seen as the progenitors of fireballs and thunderstones, long before Mr Chladni’s more rational idea took hold. Peasants might have been seeing rocks falling through the sky for thousands of years, but they were convinced it was some rather cranky god who was responsible. The myth of a culpable thundergod has an ancient lineage that includes not only the Norse god Thor, but also his English equivalent Thunor, the Celtic Tanarus, the German Donar, the Hindu god Indra, and also the Hittite sky god in Asia Minor. In his manifestation as Thor particularly, this powerful, short-tempered wielder of thunderbolts was to be feared as he soared across the heavens in a chariot pulled by a pair of goats (the unforgettably named Gaptooth and Toothgnasher), thunder rumbling in his wake.
But again we have this apparent contradiction whereby despite his apparent ferocity Thor also had his Dr Jekyll persona and was also, somewhat paradoxically, the god whom the people most loved, despite, sometimes knocking them off with the odd thunderbolt. He was the slayer of serpents and giants (using his powerful hammer Mjöllnir) and so protector of mankind. In Norse mythology Thor’s popularity arose from the fact that, more than any of the other gods, he fought to defend the world against evil. So on the one hand his Mr Hide side was to be feared as he hurtled thunderbolts and thunderstones to Earth. But on the Dr Jekyll side he was the people’s god. He was trustworthy and their protector.
So, what has all this to do with the impact (pun quite intended) of large meteorites striking the Earth? What Ted Nield argues convincingly in Incoming, and which to a large degree I agree with, is that these potential objects of hideous destruction had both their good side and their bad. They were not just careless destroyers of life, the outcome of the thundergod’s irascibility. More often than not their Dr Jekyll side rose to the surface and they may well have been, perhaps rather surprisingly, the facilitators or even the creators of life. But firstly, what of their dark side?
In March 2010 Peter Schulte (Universität Erlangen-Nürnberg, Germany) had the good fortune to have an article published in the scientific journal Nature. He was not alone. Accompanying him as coauthor on the paper were another 40 scientists. The core of their argument was something that everybody thought they already knew – an asteroid (and overly big meteorite) “triggered the mass extinction” at the end of the Cretaceous Period, about 65 million years ago. The evidence was there: a layer of sediment enriched in iridium, an element only usually found in any abundance in some meteorites. That was it. After all the facts had been examined in the finest detail, a scientific consensus had been reached. Case closed. The culprit had been identified. This is, it would now appear, how science operates – no longer the heated debates, hypotheses and counter-hypotheses flying back and forth like a frenetic shuttlecock, but by a very PC non-acrimonious consensus. All very democratic, rather like the consensus reports of the IPCC and the conclusions as to what is causing global warming. Laudable, maybe, but is this really the way science is going to progress? Argue against the consensus view and the perceived rational status quo and you can end up being marginalized and finding it harder and harder to get those papers published or grants awarded. Nield argues that proving your scientific point these days “seem(s) to call on sheer force of numbers – as though democracy mattered in science.”
What irked many palaeontologist was that there were none amongst the 40 authors in the Nature article. Two months after its publication, a letter from 29 palaeontologists appeared in Nature pointing out this rather surprising lack of expertise among the authors in an article dealing with the mass extinction of organisms. Furthermore, the palaeontologists pointed out that there were a number of other equally plausible explanations for the mass extinction, ranging from changing sea levels, to volcanic activity and major climatic changes. Perhaps the asteroid was just the straw that broke the dinosaur’s back (though why the asteroid seems to have targeted some groups, like dinosaurs and ammonites, but had much less effect on birds, snakes, lizards, turtles and crocodiles is still a conundrum that the catastrophists have yet effectively to explain).
The dilemma we now face is, which group of consensus-seeking scientists to believe? Perhaps none of them – maybe we should listen to the real outcasts, those few souls who argue against a meteorite having had any effect on the mass extinction at all. The leading voice in this debate is Gerta Keller of Princeton University. When it comes to large meteorites or asteroids Keller views them as being neither good nor bad – merely irrelevant. The organisms that she studies are not the media-sexy dinosaurs, but tiny single-celled organisms called foraminifers. Small they may be, but they occur in oceans in their countless millions and form an important link low in the food chain. Moreover, they are used extensively for dating sedimentary rocks. Keller and her colleagues have shown that the large celestial body, thought to be responsible for the mass extinction and which ended its existence in a literal Earth-shattering explosion near a place called Chicxulub in Mexico, occurred about 300,000 years before the mass extinction event.
Delayed shock is one thing, but this hiatus is a trifle inconvenient for those who believe an asteroid was the villain. Keller, an avowed ‘Chicxulub sceptic’, as Nield explains, found that being able to present papers at conferences or get them published in some peer-reviewed journals, was often quite difficult. Nield himself was at the receiving end of some of the acrimony with which Keller had been targeted, after having written about her work: “I knew things were getting serious”, he writes, “when (at the end of a stabbing finger) I was told one evening that I had done a disservice to science by ‘giving the oxygen of publicity to that bloody woman".
In the heady days of the 1970s, when blaming a meteorite for the dinosaurs’ extinction was all the vogue, a Swedish scientist, Professor Birger Schmitz (University of Lund), discovered that fossil meteorites were turning up in abundance from much older (470 million year old) rocks in Sweden. The chance of finding a single meteorite preserved in rocks of this age is pretty remote. To have found ninety, as Schmitz subsequently has after more searching, is basically ridiculous. It points to a meteorite shower of epic proportions.
Surprisingly, it is possible to calculate when a meteorite was broken from its parent body. It was known that a group of stony meteorites called L-chondrites had formed from a massive breakup of an asteroid about 470 million years ago, the same age as the rocks in which the meteorites had been found. It looked as if evidence for a massive shower of meteorites having fallen to Earth at this time had been found. This, in itself, is a nice bit of research, but to cap it off, Schmitz and a group of colleagues realized that at almost exactly the same time on Earth, something very significant had been happening to the diversity of life. It had begun to accelerate with all the vigour of the Earth’s current explosive increase in human population. After pottering along at a gentle pace for about 70 million years after the initial diversification in complex life 540 million years ago, the diversity of life increased enormously at about the time that the Earth was being showered by meteorites. Life not only prospered in the oceans at this time, but for the first time millipede- and scorpions-like animals and primitive plants ventured onto the land. Nield thinks that, “(t)he coincidence of the two events is spectacular and undeniable”. True. But it doesn’t mean they are correlated.
What this reminds me of is the story, apocryphal as it may be, of the city records of Copenhagen that apparently showed that some ten to twelve years after the end of World War II there was a strong correlation between the number storks nesting in the city each year and the number of human babies born. The conclusion is obvious: more storks bringing more babies; or then again maybe more babies bringing more storks; or then again, no correlation at all. In wondering how these meteorites could have caused an increase in life’s diversity Ted Nield suggests that maybe the individual impacts might have resulted in localised destruction, but in so doing allowed new species to rapidly colonise these new environments – an opening up of ecospace and a diversification of life.
Although I think there may be more of the stork and babies to this Ordovician correlation, I feel that Nield has a point, though, in the subtitle to his book: Why we should stop worrying and learn to love the meteorite. For if we travel much deeper in time, beyond the hundreds of millions and back into the thousands of millions of years ago, indeed back to very early in Earth history, then it is not too difficult to argue that impacts from large celestial bodies were immensely good for the health of this planet. It is one of these impacts that we have to thank for bringing us strawberries and cream every year at Wimbledon, despite the weather.
A few tens of millions of years after the Earth was formed it is thought that it suffered its largest ever impact, from a Mars-sized body (that goes under the name of Theia). Not only is this thought to have ripped off a huge chunk of the nascent earth to form the Moon, but it hit the Earth with such force that it tilted the planet so that our axis, allowing for a certain degree of wobble, came to lie at about 23.4° to the plane of Earth’s orbit. And this has provided us with seasons – and so strawberries. The presence of the Moon has also meant that our days now are much longer than they otherwise would have been. The Moon, orbiting around the Earth, actually slows the Earth’s rotation by frictional drag, and over the last four and a half billion years this has lengthened our day from about 6 to 24 hours. So all in all, a Dr Jekyll of an impact.
But arguably the most important of the lot was a bombardment by comets on a truly astronomical scale, between about 4.2 and 3.8 billion years ago. We see evidence of this in the pock-marked craters on the Moon. And it is thanks to these comets that swept through the Solar System colliding with any planet or moon in their path that you can spend your summer holidays swimming in the Aegean Sea. Comets are essentially dirty snowballs, comprising a mixture of rock and ice and are thought by many scientists to have been the source of most of the water in our oceans. But more than that, comets are known to also contain organic compounds, including amino acids. These are crucial to life and are the building blocks of proteins. They have also been found in some meteorites. One which fell to Earth near the town of Murchison in Victoria, Australia in 1969 was found to contain not only amino acids but also more than 400 other different types of complex organic molecules. Is it possible, therefore, that life on planet Earth could have been seeded from outer space, brought by an incoming comet or meteorite? If so, we would have a fair amount to thank these colossal cosmic boulders for. They might bring short-term destruction and chaos to our planet, but when weighed in the cosmic balance I suspect that their good sides have far outweighed their bad.
So, thanks to cometary and asteroid impacts long ago all’s well with the world: the season-driven daffodils are shooting up in my garden; a starling arcs across the deep blue sky overhead, the sky with the bright star. Hang on. That’s not the Sun. It’s too small. What’s that doing there? It seems to be getting bigger, and bigger. Oh dear.
By Ken McNamara
The author is a Fellow of Downing College Cambridge and author of The Star-Crossed Stone (Chicago University Press).