Meteorites – Natural histories of extraordinary species that changed our world
Messages From Heaven
These lines by C.S. Lewis conjure up a rather poignant image of earth quietly absorbing an alien fragment of rock that has come from the unknown, from outer space. It’s just one example of how the mystery of meteorites has inspired art, religion, philosophy and poetry. As these unearthly objects have crashed their way into our lives, we have struggled to make sense of them in many ways. It is not just their physical presence as lumps on the ground that intrigues us. They fall so fast through our atmosphere that they often burn and glow, flashing across the heavens as streaks of light or shooting stars. Sometimes they are even accompanied by loud bangs. But what exactly are meteorites – and where do they come from?
Like frogs or butterflies, meteorites are known by different names according to which part of their life cycle they are in. They start their lives as parts of asteroids, the moon or Mars, millions of miles out in space. They are what astronomers sometimes call ‘space debris’, and orbit the sun, just as the earth and the other planets do.
While these objects are still in space, having detached from their parent body, they are called meteoroids, but once one enters the earth’s atmosphere it briefly becomes a meteor. Only once the meteor – or if it has broken up before impact, its fragments – has actually hit the earth is it finally known as a meteorite. Meteorites can vary hugely in size, from minuscule – many just a few centimetres in diameter, while ‘micrometeorites’ are microscopic – to very large indeed: the world’s largest known example, the Hoba meteorite which lies buried in the ground in Namibia, has been estimated to weigh about 60 tonnes.
Normally, when a meteoroid enters the earth’s atmosphere, the friction and pressure from the air turns it into a fireball – what we call a ‘shooting star’ – so much so that much of it burns up before it has the chance to reach the surface. Others are small enough to simply fall to the ground under the force of gravity. But a few are so large they explode when they hit the ground.
A fireball that streaked through the early morning sky, a dazzling white light that burned brighter than the sun, and a surge of heat were all followed by a huge explosion and shockwave that shook buildings and blew the glass out of windows.
Those who witnessed this event, in Russia’s Ural Mountains on the morning of Friday, 15 February 2013, must surely have thought there had been a terrorist attack or major nuclear explosion, or perhaps even that the end of the world had come.
The event was captured in the many ways the modern world can offer: some took pictures of the glowing ball of fire on their smartphones, while other videos came from dashboard-mounted cameras designed to provide evidence in the case of a car accident. This footage was distributed around the world at astonishing speed, for everyone wanted to see science fiction become fact for themselves.
For the Natural History Museum’s Dr Caroline Smith, it was one of those events when you remember exactly where you were and what you were doing:
I heard them say there had been a large explosion in a part of Russia that I knew had links with the atomic weapons programme, so my first reaction was ‘Oh my goodness – not another Chernobyl!’ I then looked over at the TV screen and saw the video of this amazing fireball; and I knew straight away that this was not some kind of fake; this was a real, spectacular meteorite. The hairs stood up on the back of my neck and I nearly spilled my coffee. For someone in my field this was simply amazing.
Astonishingly, nobody was killed, although almost 1,000 people were injured (mostly from flying glass and other debris), and over 7,000 buildings were badly damaged by the blast. Fortunately, the meteorite and its fragments had landed in a lake just outside a town in one of Russia’s less populated regions, Chelyabinsk, about 1,500 kilometres east of Moscow and close to the border with Kazakhstan. President Vladimir Putin thanked God that no one had been killed, although one ultra-nationalist Russian politician claimed that the impact was caused by an American weapons test that had gone horribly wrong.
In fact the truth was even stranger. The meteorite was later estimated to have weighed between 10 and 13 tonnes, and measured 17–20 metres in diameter. It entered the earth’s atmosphere at a speed of 65,000 kilometres per hour, and then exploded at an altitude of about 30 kilometres above the earth’s surface, generating a bright flash and a massive shockwave as it broke up into dozens of much smaller fragments.
The Chelyabinsk meteor was the largest natural object to have entered our atmosphere for more than a century. The last had been the ‘Tunguska Event’ in June 1908. This fortunately also occurred in a depopulated part of central Russia, and thus also avoided human casualties, though it did destroy an estimated 80 million trees over an area the size of Leicestershire. The Tunguska meteor was even larger than the Chelyabinsk one: an estimated 60–190 metres in diameter and equivalent to roughly 10–15 megatonnes of TNT (a thousand times greater than the Hiroshima bomb), making it the largest impact event in recorded history. So the earth appears to have had two fortunate escapes in remarkably quick succession – geologically speaking in less than a blink of an eye.
Such cataclysmic events can happen anywhere – even much closer to home. The most famous British example is the ‘Wold Cottage Meteorite’, named after the place in Yorkshire where it fell to earth, at around three o’clock in the afternoon on 13 December 1795. It came to rest on the land of Major Edward Topham, a local landowner, playwright and newspaper proprietor, and just missed hitting a young farm boy called John Shipley, who was showered with dust and mud from its impact. He was not the only witness: others talked of a dark object whizzing through the air and hearing explosions.
Although the Wold Cottage Meteorite remains one of the largest ever recorded in Britain, it was considerably smaller than the far more destructive Russian examples, weighing about 25 kilos and making a crater less than a metre in diameter. A few years after it fell, analysis showed it to be in two parts: a soil-like compound rather like kaolin (china clay), containing silicon, magnesium, iron and nickel; and a more malleable mixture of iron and nickel.
To commemorate the event, in 1799 a 7½-metre-tall, brick-built monument was erected on Topham’s land, with a plaque proclaiming:
The meteorite was bought in 1804 by the naturalist and illustrator James Sowerby for his collection of natural objects, and later acquired by the Natural History Museum, where it remains today.
Very occasionally, meteorites do hit people. In 1954 in Sylacauga, Alabama, a meteorite the size of a rugby ball crashed through a roof, bounced off a radio and hit Anne Hodges as she sat in her living room. Luckily she got away with just bruising, and the dubious honour of being the first person on record to be struck by an extraterrestrial object.
Meteorites of varying size can be found on land all over the world, and who knows how many lie under the sea. Hot and cold deserts are good places to look for them, as the meteorites are easy to spot and the climate and geography of these regions are such that they are preserved for longer periods. A sixteenth-century woodcut shows a group of farmers and their livestock prostrate on the ground as a shower of stones falls all around and over them.
Occasionally, though, we have managed to track a meteorite all the way from space to earth. Brother Guy Consolmagno, a Jesuit and an astronomer, was for twenty years the keeper of the meteorite collection at the Vatican Observatory:
The most exciting case of a meteorite that was seen to fall to earth happened in the Sudan in 2008. The meteorite was actually seen in space by a telescope, and when they calculated how close it was going to pass, they realised that its orbit was going to pass closer than a single radius from the centre of the earth – which meant that it was going to hit the earth.
But not all sightings are so trustworthy. He meets a lot of people who honestly believe they have found a meteorite: ‘There are a lot of false alarms – I’m brought rocks all the time from people who claim, “I saw this fall out of the sky and I’m sure it’s a meteorite.” And you look at it and you know it’s a terrestrial rock – we don’t call these things meteorites, but “meteor-wrongs”.’
It is very unusual for an individual to see both the meteor’s fireball streaking across the sky and then find the exact piece of rock that caused it, simply because of the scale on which the devastation would occur: ‘These things move so fast and they are so bright that we want to say they are closer and slower than they really are. People say, “I saw something about the size of a hat and it fell behind the barn.” In fact it’s probably the size of a house and fell more than 200 miles away.’
And yet many people continue to believe that they have found a meteorite, even when the evidence against (sometimes including clear evidence that the object is man-made, such as a screw or printed writing) is overwhelming. That may be because the idea of an object arriving from outer space – from ‘beyond the surly bonds of Earth’ – has always been such a tantalising one.
No wonder, then, that the sudden appearance and dramatic consequences of falling meteorites have fired our imaginations over the ages. Ever since we have known about meteorites, we have tried to understand how it is that rocks can possibly fly through the air. The Greek philosopher Aristotle, in the fourth century BC, tried to make sense of them. He reasoned that because the heavens were perfect, the idea that they would cast giant objects down upon the earth was simply absurd. Having ruled out this possibility, he wrongly assumed that they must be some kind of meteorological phenomenon: vapours in the air that had coalesced into solid form, which were then somehow blown across the surface of the earth.
Due to his profound influence on later thinkers, Aristotle’s mistaken belief in the terrestrial origin of these heavenly bodies persisted for many centuries. As late as the eighteenth century the French scientist Antoine Lavoisier, known as the ‘father of chemistry’, confidently announced: ‘Stones cannot fall from the sky, because there are no stones in the sky!’ Yet meteorites are mentioned in the Old Testament Book of Joshua, when the Amorites, enemies of the people of Israel, are killed as they flee: ‘The Lord cast down great stones from heaven upon them.’
Meteorites had long been part of the ancient Egyptian culture, perhaps because there are many examples scattered across the desert, where they are easier to find than those in the heart of forests or jungles, or ones that fall into lakes or seas. In 1911 nine tube-shaped objects were discovered in a 5,000-year-old tomb being excavated south of Cairo. They appeared to be beads, strung together with gold and jewels to make a necklace for the teenage boy buried there. Soon afterwards, tests revealed that the objects contained an unusually high concentration of nickel; but it wasn’t until more than a century later, in 2013, that scientists revealed these objects were in fact made from meteorites.
The ancient Egyptians had a single hieroglyphic symbol for ‘iron’, which encompassed all hard metallic objects, but around 3,500 years ago this changed, when a new symbol emerged. Dr Diane Johnson, from the Department of Physical Sciences at the Open University, explains: ‘From soon after the death of Tutankhamun [in 1342 BC], we see a new term for iron, and this literally means “iron from the sky”. One possible explanation is that there has been a big dramatic event like a fireball, which would make iron and the sky synonymous, with an impact crater or meteorite fragments.’
Although we cannot link this change to a specific meteorite, there is an impact crater about 45 metres across in southern Egypt, very close to the border with Sudan. The Kamil Crater was caused by an object weighing roughly 1.5 tonnes, which would have been easily observable, with a fireball accompanied by sonic booms. It has been dated as being less than 5,000 years old, which would fit with the timing of the new hieroglyph.
In such superstitious times, it is hard to overestimate just how major an impact the landing of a meteorite would have had on ordinary people, as Brother Guy Consolmagno points out: ‘In ancient times there was certainly the sense that meteorites – things that fell out of the sky – might be some kind of message from the gods.’
So were these flashes in the sky and huge, deafening bangs a sign of heavenly displeasure, or some other kind of messenger from beyond the clouds? Was earth being used as target practice by unpredictable gods? After all, stars falling from the heavens were supposed to be a sign of the end of the world, as in this chilling verse from the Second Epistle of Peter: ‘The heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.’
As human learning progressed, however, such long-held beliefs were often dismissed as ‘superstitious nonsense’. These ideas about rocks hurtling from the heavens were not something that sat easily with the rational minds that dominated European thinking during the period from the middle of the seventeenth to the end of the eighteenth centuries, known as the Age of Reason, or simply the Enlightenment.
It is not hard to understand why, as scholars began critically to examine beliefs that had held sway for so long, and to apply a rigorous analysis based on rational thinking, many ancient truths were simply swept away. And we can hardly blame the Enlightenment thinkers for dismissing what appeared to be fanciful tales of blazing rocks hurtling down from the heavens.
This was a time when seeing was believing, and evidence, usually in the form of the results of an experiment or a reliable observation, ruled. If you didn’t actually see a meteorite hit the ground, then it didn’t. People who claimed to see rocks fall from the sky were viewed in the same light as those who believed in plagues of frogs or rain made of blood. They were unreliable witnesses – usually regarded as uneducated peasants – who had let drama cloud their rational thoughts.
But meteorites don’t play by the usual rules of science, and it would be hard to imagine an experiment that might recreate the effects of a meteorite impact. So for a considerable time, they were consigned to the realm of mythology and old wives’ tales. Even Isaac Newton refused to believe in their existence, maintaining that small rocky objects simply couldn’t exist in the vastness of interplanetary space.
But one event changed all that. One day in late April 1803 the inhabitants of the commune of L’Aigle in Lower Normandy, France, heard loud crashes, as more than 2,000 rocks fell from a ‘serene spring sky’. The Académie Française, who until then had been highly sceptical of such claims, concluded, to its amazement (and some embarrassment) that the rocks had indeed come from outer space. They did so mainly because of the evidence provided by Jean-Baptiste Biot, a young physicist and astronomer who had been sent to the village to investigate this strange phenomenon. His report noted that: ‘At a time when we were … still discussing the degree of authenticity of ancient and modern stories, L’Aigle’s inhabitants and from a large area thereabout witnessed the phenomenon … with circumstances most appropriate to strike them with wonder and bewilderment.’
Following this incident, the evidence for meteorites became incontrovertible; nineteenth-century scientists simply had to face the fact that the earth was being bombarded from outer space. Accepting that grapefruit-sized meteorites fell to earth was one thing, but even as recently as the late twentieth century it has proved hard for many scientists to accept that the impact of a meteorite could wreak havoc on a truly apocalyptic scale.
But if there is one event that is, above all else, associated with meteorites, it is the extinction of the dinosaurs. These giant beasts first appeared around 230 million years ago, became the dominant life form on the planet about 200 million years ago, and ruled the world for more than 135 million years. Then, in an infinitesimally short time by geological standards, around 66 million years ago they simply vanished.
Many theories have been put forward to explain their sudden and catastrophic demise: an event that allowed birds, larger mammals and eventually human beings to thrive and become the dominant life forms on earth. Early palaeontologists – working before the advent of Darwin and Wallace’s theory of natural selection – wondered if this calamity could have been the result of the biblical Flood (especially when other cultures also turned out to have similar flood stories), while other hypotheses included volcanic explosions, rising sea levels and the shifting of the continents.
But none of these could adequately explain why the dinosaurs (and perhaps two-thirds of all the other life forms on earth) had disappeared so suddenly; nor could they account for the comprehensiveness of the catastrophe, which extended across the whole globe.
Then, in 1980, US scientist Walter Alvarez and his colleagues at the University of California, Berkeley, proposed a radical new theory to account for the extinction event itself, which also helped to explain its suddenness and global scale. They had discovered that a layer of clay near the surface of the earth, dating to the same time period as the dinosaurs’ extinction, contained unusually high levels of iridium, a metallic element very rare on earth but common in asteroids. This, they suggested, could be evidence that a massive meteorite had hit the planet.
Meanwhile, almost 4,000 kilometres to the south-east, in the Yucatan Peninsula, two geophysicists working for the Mexican state-owned oil giant Pemex had made an extraordinary discovery: a huge underwater arc which, along with a second arc on land, formed a ring roughly 180 kilometres in diameter, centred on the village of Chicxulub. It appeared to be evidence of a cataclysmic geological event – but what could have caused it?
Eventually the two groups of scientists stumbled across each other’s findings, and after careful detective work concluded that the Yucatan crater was indeed the site of a meteorite impact; an event so huge that it could have led to the extinction of the dinosaurs. The meteorite itself would have been roughly 10 kilometres in diameter, and produced the energy equivalent to 100 million megatons of TNT – roughly 200 million times as great as the 2013 Russian meteorite, and 2 million times as powerful as the biggest human bomb ever detonated.
Professor Mike Benton, a palaeontologist from the University of Bristol, believes that the impact of this massive meteorite would have been truly cataclysmic. First, there would have been a massive ‘megatsunami’, enough to flood many of the world’s low-lying coastal regions. Then, the clouds of dust and gases created by the impact would have shrouded the entire atmosphere, blocking out the sun. This would have stopped photosynthesis almost immediately, killing plants, which would mean that herbivores starved, with carnivores disappearing soon afterwards. Temperatures would also have plummeted, making the planet a very hostile place for creatures like the dinosaurs. What’s truly incredible is that the whole process may have taken place in a matter of days or even hours.
The effects of that asteroid impact on the Mexican peninsula 66 million years ago have lingered ever since, changing the course of evolution and marking the extinction of about 60 per cent of life on earth – not just the dinosaurs. Large groups of animals such as ammonites – a group of giant marine invertebrates – also disappeared at the same time.
Yet the Yucatan meteorite crater is by no means the biggest of its kind. Scientists have recently discovered twin scars in Australia’s outback which mark the impact of a truly enormous meteorite. It may have split in two before it hit the earth more than 300 million years ago and left a crater 400 kilometres wide, the largest ever found, though there is still some debate over the interpretation of these results.
For anyone still unconvinced about the power of the meteorite, the briefest look at the pockmarked face of the moon offers conclusive proofs that large and damaging rocky missiles are flying around us. This has not gone unnoticed by science-fiction writers. The vulnerability of our tiny earth, with its fragile inhabitants whirling in the dark vastness of a hostile universe is just too good a theme to ignore. H.G. Wells’s 1897 short story ‘The Star’ was written nearly a century before the effects of the Yucatan meteorite were understood. It describes the near impact of a huge meteor that streaked past earth, heating it up and causing all kinds of mayhem:
And then the clouds gathered, blotting out the vision of the sky, the thunder and lightning wove a garment round the world; all over the earth was such a downpour of rain as men had never before seen, and where the volcanoes flared red against the cloud canopy there descended torrents of mud. Everywhere the waters were pouring off the land, leaving mud-silted ruins, and the earth littered like a storm-worn beach with all that had floated, and the dead bodies of the men and brutes, its children. For days the water streamed off the land, sweeping away soil and trees and houses in the way, and piling huge dykes and scooping out titanic gullies over the country side. Those were the days of darkness that followed the star and the heat. All through them, and for many weeks and months, the earthquakes continued.
As Mike Benton has shown, H.G. Wells wasn’t far off the mark. Even though today we know considerably more about meteorites, it doesn’t stop our imaginations working overtime. Scientists now generally accept that a meteorite played a major part in the extinction of the dinosaurs, and therefore, by default, in our current dominance of the planet. But could a meteor one day also be the reason our own species disappears from earth?
The idea that the end of the human race will come about as the result of an object from outer space has long been a staple of Hollywood disaster movies, from When Worlds Collide in 1951, through Meteor in 1979, to two blockbusters in 1998 – Deep Impact and Armageddon. And yet the events of 15 February 2013, when the Chelyabinsk asteroid was not even detected until it was close to the ground (partly because it came out of the same sector of the sky as the sun), serve to remind us that meteors can and do hit the earth from time to time. Just because there were no fatalities then doesn’t mean that next time we will be so lucky. And as the events of 66 million years ago show, the effects of a meteor hitting the earth can, if it is big enough, change the course of history.
In spite of all we have learned about them, some people would still like to believe that meteorites are personal messages from a huge, dynamic universe, or, at the very least, the bearers of extraterrestrial life forms. Modern myths are still being propagated, including one related to a very unworldly-looking plant, the carnivorous Venus flytrap. This unusual species feeds entirely on small insects that are caught by the closing of the hinged ‘jaws’ of the plant’s modified leaves, where they are gradually dissolved and subsumed. Like other carnivorous plants such as our own native sundew, the Venus flytrap evolved to survive in boggy areas with low amounts of nutrients – especially nitrogen. Eating insects was a viable way to obtain what it needed to survive.
But confronted with the Venus flytrap, with its odd appearance and even more bizarre habits, our ancestors formulated a myth that it came from another world, as Nick Johnson, from the Royal Botanic Gardens at Kew, explains:
There are stories that suggest that these plants were some kind of ‘cosmic hitchhikers’, cadging a lift on a meteorite. This probably arose because Venus flytraps do admittedly often grow on the edge of depressions, between boggy areas and grasslands, which may have led our ancestors to jump to the conclusion that these were craters left by meteorites.
However, as Nick Johnson points out, when you examine the DNA evidence then this theory soon falls apart, as the Venus flytrap is closely related to other members of the sundew family.
Even in the face of scientific progress, however, we do like to maintain a little mystery. The late Terry Pratchett used meteorite iron in his hand-made sword, and if you fancy forging your own weapon, you may be interested to hear that many people do buy fragments, believing in their healing properties. Beth Holtum and her husband Graham run a shop selling all kinds of crystals and meteorites in Wadebridge in Cornwall. The various meteorites and tektites, the glassy rocks usually found some distance from an impact crater, are claimed to have different properties from increasing spiritual awareness to aiding healing.
When we interviewed her, Beth was wearing a necklace of green tektites, gathered from a meteorite crater, which she described as: ‘A very active stone from a crystal healer’s point of view. It will raise one’s spirits; one feels lighter, which may be because of the contrast with the heavy meteorite.’ Today’s belief in the healing properties of meteorites is, she says, a continuation of ancient beliefs going back hundreds of years. ‘For many centuries, different civilisations have looked at stones that have landed from somewhere else, and realised that by holding an item you can actually pick up on the past events it has experienced, in a process known as “vibrational healing”.’
Scientists may dismiss this as ‘New Age nonsense’, but our fascination with meteorites lingers. Steven Spielberg, director of E.T. and Close Encounters of the Third Kind, recalls a childhood event that cemented his fascination for extraterrestrial objects:
My dad took me out to see a meteor shower when I was a little kid, and it was scary for me because he woke me up in the middle of the night. My heart was beating; I didn’t know what he wanted to do. He wouldn’t tell me, and he put me in the car and we went off, and I saw all these people lying on blankets, looking up at the sky.
Spawning speculation and sensation throughout the centuries, meteorites will always hold us in thrall. They are literally otherworldly, visitors from an alien realm. They may heal us – or they may not – but their bigger relatives may determine no less than the future of our planet and its inhabitants.
Full fathom five thy Father lies;
And of his bones is coral made;
Those are pearls that were his eyes,
Nothing of him that doth fade
But doth suffer a sea change
Into something rich and strange.
William Shakespeare, ‘Ariel’s Song’, The Tempest