Four and a half billion years ago, all the atoms now locked up in the asteroids and planets of our solar system— including the atoms that make up you— swam freely in a huge disk-shaped cloud of dust and gas. The cloud, called a nebula, progressed majestically around our infant sun like a giant record played at slow speed— until something happened: a genesis moment. For reasons still mysterious, the nebula coalesced, becoming rocky and lumpy. Gravity accreted larger and larger chunks until, in just a few million years, the ancestral cloud transformed itself into asteroids and planets, including the one we evolved on. But even Earth's most evolved brains still haven't grasped why space dust condensed into boulders. The moment was hugely important— it's our creation story— but the evidence to describe it is fragmentary. All we have are several dozen rare and perplexing meteorites, remnants of ancient asteroids that intersected our planet's path and streaked through the sky to land on Earth, after floating in space since the rocky beginnings of our solar system.
|Carbonaceous chondrites, so vital to planetary science, are as scarce as hen's teeth here on Earth. But geologist Philip Bland of The Open University in Milton Keynes, England, has determined that Mars may be littered with as many as 200,000 meteorites per square mile— a significant percentage of which may be these rare, coveted rocks.|
Photo by Alastair Thain
These meteorites, called carbonaceous chondrites, contain the truth about how our solar system evolved, but interpretations of their evidence seem contradictory. On the one hand, carbonaceous chondrites have roughly the same chemical makeup as the sun, which suggests they are pure remnants of that ancient nebula locked in a rock. On the other hand, they show evidence of geological alteration, which means they have changed over time. But, if they're altered, they should no longer look like pure nebula. Science cannot proceed past a paradox; until this one is solved, the origin of the planets will remain a mystery.
Studying ancient meteors is rather like being a priest in the temple of Apollo, the sun god— you must wait for the stones to fall from the heavens to serve as your oracles. In this science you can't breed more rats or order more reagents. You cannot re-create the nebula in an experiment. Rather, you must imagine how the planets formed and search for a convincing way to test that theory with evidence culled from a handful of space rocks. That is exactly what 32-year-old geologist and planetary scientist Philip Bland, a research professor at The Open University in England, set out to do. Intrigued by a theory that Oxford geologist Edward Young proposed in the journal Science,
Bland decided that it would be possible to figure out how carbonaceous chondrites came to be geologically altered without losing their solar purity.
Philip Bland's most cherished childhood memory comes from a stormy morning when his mother woke him and his sister early, dressed them warmly, and rushed them out of a small vacation farmhouse in Wales to a windy bluff overlooking the sea. She wanted them to stand witness to the tempest. "I'm this little 7-year-old guy, and my sister's tiny, and the waves are 20 feet tall. But there was nothing scary about it— it was just beautiful." The boy saw the look of rapture on his mother's face, and he came to love nature as his mother did, for its sublime beauty. But where Bland's mother stood before nature and worshipped its power, young Phil dove in with a child's unfettered curiosity. He searched for fossils, for example, with such concentration that he often lagged behind on school outings. His teacher dismissed his efforts: "Look at Phil, everybody— always playing with rocks." He smiled politely but kept right on searching. His mother encouraged his obsession, obtaining for him his greatest treasure, a set of geological maps of the county where they lived— Derbyshire, in the north of England.
Phil's father also poured energy into nurturing the boy's interests. A mild but independent man who despised his job as an electrician at the Rolls Royce airplane engine factory, he was, Bland says, "not cut out for the bureaucracy of bosses." He taught Phil to love tools, how to handle them and make them do his bidding. They spent all their weekends building: a garage for the family car, an elaborate hutch for the "monstrous rabbit" they had inherited, countless shelves and cabinets.
Phil couldn't stay forever wrapped up in the safe and happy world his parents created at home, but it wasn't clear what he might do with his life. No one in his family had gone to college, and no one expected him to go. When he got into the University of Manchester, he decided to attend not because he wanted to pursue science, but because he feared the alternatives: "the civil service or working for Rolls Royce."
At Manchester, he fell in love with geology and began to glimpse an escape route that might take him beyond Derbyshire. "When I go to the mountains of Scotland, I know that the rock I eat my lunch on is two and a half billion years old. That's more than half the age of the Earth. I know the incredible forces that made it. Knowing that adds another layer of beauty to an already beautiful thing." By the time he graduated, he thought he knew what he wanted from life: to eat his lunch beside those mountain rocks and study their morphology.
Although he was determined to tackle a doctorate, money was a problem. Fellowships for Ph.D.'s in England are few. "The bank was already after me," he says, "for loans I'd had from my undergrad days." Rather than risk going further into debt, he felt he had no choice but to get a job, so he grabbed the only interesting geology position he could find: curator of meteorites at The Open University's museum in Milton Keynes, an hour northwest of London.
He didn't know much about meteorites, but he was "always interested in geeky space stuff," so he began to read everything about them he could find. It frustrated him that although there were records of where and when many of them had been found, no one knew how much alteration they had undergone while sitting here on Earth. Bland saw that he could figure this out using a Mossbauer spectrometer, a simple tool researchers have relied on for more than 40 years, to analyze mineral content. Over time, geological forces— heat, water flow, and pressure— alter the structure of minerals, and a Mossbauer spectrometer can quantify the degree of alteration by detecting the transfer of electrons that accompanies structural changes.
The longer a meteorite has been down, Bland reasoned, the longer it has been subjected to the ravages of Earth's climate, especially exposure to rain. He began to analyze meteorites, looking for minerals that change as a result of water flow in rock, a process geologists call aqueous alteration. Then he began to track minerals common in meteorites, such as iron nickel, which turns slowly to magnetite over centuries in the presence of water. Using his Mossbauer, Bland determined the ratio of magnetite to iron nickel in each meteorite. The higher the ratio, he figured, the more alteration it had undergone, and, therefore, the more weathering it had seen on Earth.
He also realized that, if he counted the number of meteorites in a given area and matched that against how weathered they were, he could calculate precisely how many had fallen in that region in a given period. His results provided the first hard evidence that meteorites were falling at a constant rate— roughly 100 meteorites weighing more than 10 grams per 40 million square miles per year— over the last 50,000 years.
|To identify and quantify amounts of minerals in meteorites, Bland relies on an X-ray diffractometer.|
Photo by Alastair Thain
Planetary scientists at The Open University were impressed. They saw immediately that Bland's work had done far more than quantify the weathering of the meteorites in their collection. He had pioneered a methodology. Meteorites are often finely grained rocks, difficult to analyze with geological tools that were designed to study coarser Earth rocks. Refining these instruments to examine meteorites was a task Bland was ideally suited for because of the years he had spent under his father's tutelage. The department encouraged him to write up his work as a master's thesis. When he handed it in, they awarded him a doctorate instead. "I got a bargain Ph.D.," he recalls. It was 1995, and he was only 26.
Still, success was bittersweet. Having moved from mountains to meteorites, Bland had few credentials or references. His prospects for a postdoctoral appointment or an academic job were not good. Failing to find a university position made him wonder if the system were set against sons of factory workers. A friend and colleague at The Open University, Anna Butterworth, says: "Phil thought that if he'd gone to Oxford or Cambridge, it would have been easier for him. I had another friend who had gone to Cambridge, and Phil hated him, made fun of his 'Cambridge' accent. It's the only time I've ever known Phil to dislike someone."
Doggedly committed to the study of meteorites, Bland cobbled together short-term projects. "He applied for every grant there was," Butterworth says. "He got rejected by the first 10. The rest of us would have quit, but he kept applying and finally started getting them."
Between grants, he supported himself by working as a carpenter and a software designer. He attended meteorite conferences when he could afford them and began correspondences with meteoriticists. Many seemed drawn to him by his independent thinking and enthusiasm. Bland is "bumptious," says the more sober Edward Young, "but not to a fault. He is also a remarkably intelligent and self-effacing guy, a 'normal Joe.' His manner of speaking is very down to earth, yet when he talks at a scientific meeting, you realize how much lies behind this facade."
Bland's hand-to-mouth life grew dreary. He doubted he would ever get an academic position, but he resolved to keep studying meteorites. "I was friends with a guy who had a Mossbauer, so I could still have used that to run my data and do the science in my spare time," he says. He began to see himself as a carpenter-scientist, an idiosyncratic vision he might well have lived out had his obsessive thinking not led to a few remarkably good ideas. Those ideas in turn led to a research position at the Natural History Museum in London.
Trying to figure out how our solar system formed by looking at meteorites can be tortuous. Try, for example, to follow these three statements: One, the 30 or so carbonaceous chondrite meteorites well-preserved enough to be worth studying may not be identical, but they all have roughly the same chemical composition— the same chemical elements in the same proportions— as our sun. Two, the sun's chemistry should be the same as the chemistry of the original nebula because it, too, was formed from the nebula. Three, carbonaceous chondrites are therefore pure nebular material (syllogism: If the sun and the nebula are the same, and the sun and the meteorites are the same, the meteorites and the nebula must be the same). One set of chemical ingredients in these meteorites— volatiles— supports this syllogism particularly well: Carbonaceous chondrites contain volatiles in amounts and proportions similar to those found in the sun— while other meteorites do not. However, volatile elements are highly soluble in water, so rain, especially in hot climates, will remove them from rocks. Yet analysis has demonstrated that the minerals in carbonaceous chondrites have been transformed by water flow in space. So there's the enigma: Why didn't the water remove the volatiles?
Once he was ensconced at the Natural History Museum, Bland devoted himself to solving this puzzle with his trusty Mossbauer— he now had his own machine whirring away in his lab. Although geological alteration in carbonaceous chondrites had been established, a full accounting of their mineral content had not. "At a very basic level, we knew what kind of stuff was in there," Bland explains, "but I was surprised to find that no one really knew in what proportions this stuff was present." At that point, Bland happened upon Ed Young's paper.
Looking closely at differences among various carbonaceous chondrites, Young had paid special attention to both their chemistry and their geology. An expert on oxygen, which is volatile when contained in these meteorites, he compared the amount of different isotopes of oxygen (oxygen of different weights: 16
O) to the amount of alteration in each meteorite using a computer model. In his projection, he saw something no one had noticed before: The percentage of oxygen of heavier atomic weights in any given carbonaceous chondrite was directly proportional to the amount of alteration it had undergone: the more alteration, the more heavier-weight oxygen was present. This would be consistent, Young argued, only if water was flowing through the rocks, leaving more of the heavier isotopes behind. Bland was amazed. Volatile content and geological alteration were directly proportional? Chemistry and geology no longer looked contradictory, but causal. If this was true for all volatile elements, Bland reasoned, then the chemical purity of the nebula found in carbonaceous chondrite meteorites was not there in spite of the alteration. It was there because of it. End of paradox.
|He uses a mass spectrometer— tailored to his specifications by two researchers in his lab— to measure mineral alteration in minute meteorite fragments.|
Photo by Alastair Thain
Bland phoned Young excitedly. "It was such a buzz!" he recalls. They discussed what it would mean if Bland could find hard evidence for all volatiles. If geological alteration really added volatiles to rock, rather than removed them, they had to explain how that could happen. It turned out that it wasn't so difficult to imagine. Instead of seeing each meteorite as a closed system, an isolated and conserved piece of nebula, Bland and Young imagined each meteorite as an open system subject to weathering in space. They speculated that, as the nebula accreted, different types of elements banded together separately. Like oil and vinegar separating from each other, nonvolatile elements condensed into rocky minerals while volatile elements froze in ice. Such a separation is not a stretch because elements tend to bond together in this fashion on Earth— that can be shown in a lab. Over the course of an asteroid's life, Bland and Young reasoned, a meteorite would have been subjected to heat as a result of radioactive decay within the rock, which would cause the volatile-rich ice to melt and flow. That flow altered the minerals in the rock without drawing off the volatiles because they were not in the rock in the first place; they were in the ice. Since altered minerals are more claylike and "sticky," as Bland puts it, the volatiles in the flowing water tended to lodge in the sticky mineral and stay there. Thus, the more alteration, the richer in volatiles the asteroid became.
It was a neat idea, crowned with the theoretical elegance that scientists love and which prior theories had lacked. Its implications challenged fundamental beliefs in the field. Meteorites that appear radically different in nature may, in fact, have split off the same parent body and been changed by weathering in space— after their formation. However, neat ideas aren't the same as accepted theories. Evidence was needed. Bland had to go back to the meteorites and demonstrate a relationship between volatiles and alteration across all carbonaceous chondrites.
Months later, sitting chair-tired in his basement office in the museum one afternoon last year, Bland was floored as his computer spit out its results. "Wherever I looked, [volatile] abundances and alteration lined up. Straight lines. So of course I thought I'd screwed up," he remembers with a slight smile about his lips. "Then I realized what I was seeing." The amount of volatiles in the meteorites— and, therefore, their claim to nebular composition— was in direct proportion to the extent of their geological alteration. The data provided strong evidence that geological alteration had put the volatiles there. "It was just beautiful. Just like looking back in time at the nebula, you know? People have been working for donkey's years to figure out this stuff, and there it was, right in front of me, a fundamental process of nature that no one's ever seen before— if I'm right."
If he's right, carbonaceous chondrites are, after all, reliable oracles, and geology no longer contradicts chemistry. Time— and a good deal more hard work— will tell. Others must replicate the findings. But, eventually, we will know whether Bland's data makes other theories, in Young's words, "superfluous— even fatuous." If he is right, scientists can begin to investigate the mysterious genesis process that gave birth to a planet that evolved creatures who could investigate events 4 billion years old.
Bland himself regards his own investigations from the healthy perspective of a geologist who thinks in eons. "It's dangerous to assume that there's some end to this process," he says, "that any current scientific understanding holds some special place. The folks that come after us will use some of our stuff, dustbin some of it, and get a bit closer to the way things are."
For a great place to begin learning about meteorites, see The New England Meteoritical Services home page at www.meteorlab.com/homepage.htm