by Kevin Krajick, Columbia University
Apr. 8, 2013 (TSR) – Scientists examining evidence across the world from New Jersey to North Africa say they have linked the abrupt disappearance of half of earth’s species 200 million years ago to a precisely dated set of gigantic volcanic eruptions.
The eruptions may have caused climate changes so sudden that many creatures were unable to adapt—possibly on a pace similar to that of human-influenced climate warming today.
The extinction opened the way for dinosaurs to evolve and dominate the planet for the next 135 million years, before they, too, were wiped out in a later planetary cataclysm.
In recent years, many scientists have suggested that the so-called End-Triassic Extinction and at least four other known past die-offs were caused at least in part by mega-volcanism and resulting climate change. However, they were unable to tie deposits left by eruptions to biological crashes closely in time.
This study provides the tightest link yet, with a newly precise date for the ETE—201,564,000 years ago—exactly the same time as a massive outpouring of lava.
“This may not quench all the questions about the exact mechanism of the extinction itself. However, the coincidence in time with the volcanism is pretty much ironclad,” says coauthor Paul Olsen, a geologist at Columbia University’s Lamont-Doherty Earth Observatory, who has been investigating the boundary since the 1970s.
The new study, appearing today in an early online version of Science, unites several pre-existing lines of evidence by aligning them with new techniques for dating rocks.
Finding dates
Lead author Terrence Blackburn (then at Massachusetts Institute of Technology; now at the Carnegie Institution) used the decay of uranium isotopes to pull exact dates from basalt, a rock left by eruptions. The basalts analyzed in the study all came from the Central Atlantic Magmatic Province (CAMP), a series of huge eruptions known to have started around 200 million years ago, when nearly all land was massed into one huge continent.
The eruptions spewed some 2.5 million cubic miles of lava in four sudden spurts over a 600,000-year span, and initiated a rift that evolved into the Atlantic Ocean; remnants of CAMP lavas are found now in North and South America, and North Africa.
The scientists analyzed samples from what are now Nova Scotia, Morocco, and the New York City suburbs. (Olsen hammered one from a road cut in the Hudson River Palisades, about 1,900 feet from the New Jersey side of the George Washington Bridge.)
Previous studies have suggested a link between the CAMP eruptions and the extinction, but other researchers’ dating of the basalts had a margin of error of 1 to 3 million years. The new margin of error is only a few thousand years—in geology, an eye blink.
Blackburn and his colleagues showed that the eruption in Morocco was the earliest, with ones in Nova Scotia and New Jersey coming about 3,000 and 13,000 years later, respectively. Sediments below that time contain pollen, spores, and other fossils characteristic of the Triassic era; in those above, the fossils disappear.
Among the creatures that vanished were eel-like fish called conodonts, early crocodilians, tree lizards, and many broad-leaved plants.
The dating is further strengthened by a layer of sediment just preceding the extinction containing mineral grains providing evidence of one of earth’s many periodic reversals of magnetic polarity. This particular reversal, labeled E23r, is consistently located just below the boundary, making it a convenient marker, says coauthor Dennis Kent, also at Lamont-Doherty.
With the same layers found everywhere the researchers have looked so far, the eruptions “had to be a hell of an event,” says Kent.
The third piece of chronological evidence is the sedimentary layers themselves. Sedimentary rocks cannot be dated directly—one reason why the timing of the extinction has been hard to nail.
Only 20,000 years
Olsen and some others have long contended that the earth’s precession—a cyclic change in the orientation of the axis toward the sun and resulting temperature changes—consistently created layers reflecting the alternate filling and drying of large lake basins on a fairly steady 20,000-year schedule.
This idea is well accepted for more recent time, but many scientists have had doubts about whether it could be applied much farther back. By correlating the precisely dated basalts with surrounding sedimentary layers, the new study shows that precession operated pretty much the same way then, allowing dates with a give or take of 20,000 years to be assigned to most sediments holding fossils, says Olsen.
Olsen has painstakingly cataloged the layers around the time of the End Triassic, and the initial phase of the extinction occurs in just one layer—meaning the event took 20,000 years at most. But, he says, “it could have taken much less. This is the level of resolution we have now, but it’s the ‘less’ part that is the more important, and that’s what we are working on now.”
Many scientists assume that giant eruptions would have sent sulfurous particles into the air that darkened the skies, creating a multi-year winter that would have frozen out many creatures.
A previous study by Kent and Rutgers geochemist Morgan Schaller has also shown that each pulse of volcanism doubled the air’s concentration of carbon dioxide—a major component of volcanic gases.
Following the cold pulses, the warming effects of this greenhouse gas would have lasted for millennia, wiping out creatures that could not take too much heat. (It was already quite hot to begin with at that time; even pre-eruption CO2 levels were higher than those of today.)
Fossils show that heat-sensitive plants especially suffered; there is also evidence that the increased CO2 caused chemical reactions that made the oceans more acidic, causing populations of shell-building creatures to collapse. As if this were not enough, there is also some evidence that a large meteorite hit the earth at the time of the extinction—but that factor seems far less certain.
A much stronger case has been made for the extinction of the dinosaurs by a meteorite some 65 million years ago—an event that opened the way for the evolution and dominance of mammals, including human beings. Volcanism may have been involved in that extinction as well, with the meteorite delivering the final blow.)
The End Triassic was the fourth known global die-off; the extinction of the dinosaurs was the fifth. Today, some scientists have proposed that we are on the cusp of a sixth extinction, this time caused by humans.
Today’s Earth
Explosive human population growth, industrial activity, and exploitation of natural resources are rapidly pushing many species off the map. Burning of fossil fuels in particular has had an effect, raising the air’s CO2 level more than 40 percent in just 200 years—a pace possibly as fast, or faster, than that of the End Triassic.
Resulting temperatures increases now appear to be altering ecosystems, and CO2 entering seawater is causing what could be the fastest ongoing acidification of the oceans for at least the last 300 million years, according to a 2012 study.
“In some ways, the End Triassic Extinction is analogous to today,” says Blackburn. “It may have operated on a similar time scale. Much insight on the possible future impact of doubling atmospheric CO2 on global temperatures, ocean acidity, and life on earth may be gained by studying the geologic record.”
Additional authors of the study contributed from MIT, Rutgers, Grand Manan in New Brunswick, Canada, Stony Brook University, and Université Mohammed Premier in Oudja, Morocco.
BACKGROUNDER: THE FOURTH EXTINCTION
Over the past 450 million years, life on earth has undergone at least five great extinctions, when biological activity nosedived and dominant groups of creatures disappeared. The final one (so far) was 65 million years ago, when it appears that a giant meteorite brought fires, shock waves and tsunamis, then drastically altered the climate. That killed off the dinosaurs, setting the stage for mammals—and eventually us—to evolve. Many scientists are now starting to think we are on the edge of a sixth extinction—this one driven by human destruction of other species and their habitats, and our quickening releases of carbon dioxide into the air, which threatens to bring another round of rapid climate change.
The causes of the fourth extinction—the one that paved the way for the dinosaurs—are a mystery. This is the province of paleontologist Paul Olsen and geologist Dennis Kent of Columbia University’s Lamont-Doherty Earth Observatory. They have been studying it for decades. After gathering clues from sites including ancient lava flows in Morocco, wave-washed sea cliffs along the coast of Wales, and in rocks deep beneath the modern landscapes of New Jersey and Pennsylvania, they may be getting closer to an answer—one that could have parallels to today.
This Triassic-Jurassic extinction (also known as the End-Triassic)—happened 201.4 million years ago. It wiped out half the species on earth: eel-like fish called conodonts; mammal-like swamp-dwelling therapsids; early crocodilians; monkey-faced tree-dwelling lizards; many broad-leaved plants; and others. Dinosaurs were until then a relatively minor group, but hung on and subsequently evolved rapidly in size and diversity. Until recently, the exact timing remained murky, but by 2002 evidence from fossils and other sources showed it was extremely sudden—spanning just a few thousand years or maybe less, at 201.4 million years ago. As for the causes, among other things, scientists have contemplated gradual shifts in climate and sea levels that reached a deadly tipping point. However, bets today have shifted to massive volcanic eruptions that alternately cooled and heated the atmosphere with soot and carbon dioxide—much like human pollutants today. Recently, Olsen and Kent have introduced another possibility: a meteorite like the one that killed the dinosaurs. But evidence for all the ideas remains incomplete. “The only thing we can say for certain about the Triassic-Jurassic extinction is that it happened,” said Olsen. ”It could have happened over 10,000 years, or it could have happened in a day.”
The two researchers have been at this for a long time. When Olsen was 14, he and a friend heard that dinosaur footprints had been discovered in a quarry near their suburban New Jersey home. They raced over on their bikes. The boys were soon cataloging thousands of fossils and footprints from the late Triassic and early Jurassic. In the course of a successful public drive to preserve the quarry, the teen Olsen appeared in Life magazine and got a commendation from then-president Richard Nixon. He went on to become a leading paleontologist. Kent, also from New Jersey, is a top expert in dating ancient events using periodic reversals of earth’s magnetic field, which are preserved in rocks. He is a pioneer in the field on many levels. In 1977, he published one of the first papers showing that the extinction associated with the end of dinosaurs was very sudden, helping set the stage for the later acceptance of the meteorite theory, around 1991. Last year, he coauthored a study pushing back the date of the earliest sophisticated human tools in east Africa to 1.8 million years ago.
In 2002, Olsen and Kent coauthored a paper in the journal Science showing that large dinosaurs showed up in what is now New Jersey just 10,000 years after the Triassic extinction. Moreover, they showed that rocks from that time contain a spike of iridium—an element rare in earth’s crust, but abundant in meteorites. Could an earlier meteorite have cleared the way for the dinosaurs, as well as having later killed them off? (It was a separate layer of iridium found by other researchers that helped clinch the meteorite theory of the dinosaurs’ demise.) Soon, other researchers found seemingly related evidence near the Triassic-Jurassic boundary, including roughly matching iridium layers in Morocco and Nova Scotia, and quartz in Italy apparently shattered by some gigantic impact. But the case was inconclusive; for one thing, there was no known meteorite crater from that time big enough to have spread such an iridium layer, nor caused global damage.
Meanwhile, Kent, Olsen and others began to build the case for volcanism. Roughly concurrent with the extinction, the single giant continent of Pangaea, then comprising most of earth’s landmass, began splitting up. One rift evolved into the Atlantic Ocean, as new continents moved apart; this was accompanied by repeated massive outpourings of lava over hundreds of thousands of years, forming the Central Atlantic magmatic province—igneous rocks that underlie today’s coasts of eastern North America and parts of Brazil and west Africa. Sulfur particles from eruptions would have darkened skies for years, chilling the planet. Such particles settle quickly, but another major component of volcanic eruptions is carbon dioxide, which stays in the air for centuries, warming it up. Thus, alternate chills and heat waves would have prevailed.
Kent and Olsen have gathered perhaps the clearest evidence of such a scenario so far. Last year, in another Science paper, they showed that lava flooded what is now the U.S. northeast several times in spurts separated by about 200,000 years each. Using deep drill cores penetrating below today’s heavily settled landscape, they have analyzed those lava sheets, along with intervening layers of ancient soils built up during pauses in the volcanism. The soils, they found, contain spikes of carbon dioxide five to ten times the levels of today—enough to kill off much plant and animal life with excess heat, and acidify the oceans with chemical reactions. “The flipping back and forth between extremes of hot and cold, quite possibly would be worse than either one alone,” said Olsen. The earliest lavas in the U.S. northeast seem to come about 10,000 years after the sharp extinction boundary, so it is hard to show a connection there; but lavas in the Atlas Mountains of Morocco that Olsen has sampled seem to coincide directly with it. This year, the scientists drilled more cores in New Jersey in an attempt to refine their data.
In 2010, the meteorite idea popped up again, when a separate research group re-dated a badly eroded meteorite crater near Rochechouart, western France, previously thought to be 214 million years old. Instead, they found it is 201.4 million years old—exactly matching the T-J boundary. The crater is only a sixth the size of Mexico’s Chicxulub crater, which is correlated with the dinosaurs’ demise, and probably not big enough to cause global catastrophe—but enough to intrigue Olsen and Kent. They have been drawn also by accounts of recently identified sedimentary rocks along sea cliffs in England, Wales and Northern Ireland from the same time. One layer seems to have been formed or altered by some giant tsunami or earthquake—a possible product of the impact. “We still favor volcanism, but a role for a meteorite in softening up ecosystems for the onslaught that followed is not impossible,” said Olsen. “At this point, we have a big hole; evidence of shaking; an iridium layer; and a disappearance, all around the same time. But we don’t know if it was at exactly the same time.” As Kent told Nature reporter Roff Smith: “The only way we are ever going to be able to unravel this mystery is to work out a timeline, as precise as we can make it, of all the various events around the world that led up to it.”
In 2011, Kent and Olsen headed to the United Kingdom to investigate how the rocks there relate to the extinction—specifically, whether they contain an iridium spike indicating a meteorite strike. Olsen has also visited the Atlas Mountains of Morocco, where giant sheets of volcanic basalt and other rocks dating to this time lie exposed. In 2012, they also returned to a site that is a staple for college geology-class field trips: a rock layer in Exeter, Pa., that is one of the few places where the sharp but often deeply buried Triassic-Jurassic boundary is clearly visible to the naked eye and easily accessible. The layer sits exposed in a bluff near a housing development. They hope to drill this site as well.
Whatever the exact mechanisms of the extinction, the researchers see parallels with today. Rapid changes to the atmosphere, including massive carbon dioxide releases, obviously took a toll—possibly on time scales similar to our own current boom in carbon-dioxide production and the resulting warming of the world. “There probably are very significant lessons to be learned about processes in the doubling of CO2,” said Olsen. “We have to get, however, the pattern, and the basic chronology and the basic history right first, before we try to learn great lessons about what lies ahead for us in the future.”
The Triassic and Today: Hinge Points in Earth’s History
Paleontologist Paul Olsen has been investigating the causes of Triassic-Jurassic extinction–a turning point in earth’s history that wiped out many life forms and started the reign of dinosaurs. More than 200 million years separate us from this catastrophe (also called the End-Triassic Extinction), but it could contain some lessons for us today, says Olsen. For one, it may have been caused in part by massive volcanism that pumped large amounts of carbon dioxide into the air, and in turn brought on rapid warming of the global climate. This might be compared in some ways to manmade increases in CO2 today. Recently, Olsen was chiseling out Triassic rocks that lie along what is now the low-tide line on the coast of southern Wales. He took a break to speak with Earth Institute science journalist Kevin Krajick about life and death in those ancient times.
What was the upshot of the End-Triassic Extinction?
In a very basic way, we want to know why about 50 percent of life forms died out, both in the marine realm and in continental environments. And here in Wales and in other places in the UK, the marine successions allow us to look very precisely at that transition. And there are other features such as earthquake-deformed sediments that we think can tell us what caused that mass extinction–whether it was volcanic eruptions, or it was a combination of volcanic eruptions, and perhaps an asteroid impact.
What sorts of life forms existed before, and what kinds existed afterward?
In the marine realm, there was a large diversity of molluscs, particularly cephalopods called ammonites, with coiled shells, very well ornamented, very easy to identify. They almost go entirely extinct, with only maybe one or two forms making it across the extinction level. On the continents, you had lots of crocodile relatives–terrestrial forms that were both plant-eaters, some of them, and carnivores [and] others, [and] were the dominant continental forms, with dinosaurs comprising a relatively small part. The crocodilian relatives almost all become extinct, except for the ancestors of true crocodilians, which of course prospered later on. Dinosaurs became far more abundant after the extinction, where they were relatively rare beforehand. So this is one of the great turning points in earth’s history, where you have the establishment of the real age of dinosaurs after this gigantic mass extinction.
So why did the dinosaurs take over–what was it that allowed them to become dominant?
Something akin to luck probably allowed the dinosaurs to survive and take over. Crocodilian relatives, they may have been living at higher latitudes and were susceptible to the environmental changes that occurred at the end of the Triassic. Especially extreme global warming and maybe short but important episodes of cold as well.
So you think it was the heat that did them in? Heat and/or cold?
My prejudice is that the heat was probably the more important, but certainly if volcanic eruptions or an asteroid [produced] short periods of cold followed by longer periods of extreme warmth, that combination is sort of like a one-two punch that would make it very difficult for creatures that weren’t able to [take] large swings in climate to survive.
How hot did it get, and how cold might it have gotten?
We don’t have any real way of directly measuring temperatures. We do know that plants suffered extinctions in groups that tended to have large leaves. And that’s consistent with extreme heat, lethal heat perhaps, in the 50 degrees Centigrade [120 degrees Fahrenheit] range. Cold, we don’t have any direct way of measuring that either. We do know that crocodilians and their relatives were probably very sensitive to cold, but we don’t know how cold it got. There’s no evidence of ice, for example, but that doesn’t mean it couldn’t have existed for short periods of time.
The heat was caused by what you believe was rising carbon dioxide, right? Let’s talk about that briefly.
Sure, There’s pretty convincing evidence, both from soil carbonates and plant leaves and cells that CO2 was double to triple during the extinction levels as it was beforehand, and that that was probably the origin of extreme heat.Now, there’s a lot more work to be done in that direction. We have to make sure that we understand the absolute as well as the relative magnitudes of the changes. But certainly, I think you can make a convincing case that extreme heat was very, very important in that mass extinction.
I think you’re talking about a time [when carbon dioxide] was already very high, much higher than today, and then it went even higher.
Yes, CO2 was very high to begin with, before the mass extinction. Thousands of parts per million, as opposed to hundreds now. And there’s no evidence of ice at the poles during that time at all. Zero. It’s one of the few times in history where there’s absolutely no evidence of extreme cold at the poles. So, that’s consistent with elevated temperatures already. You can imagine [in] the tropics, things are already living close to a lethal level. If you bump it up even a few degrees, it could be lethal, especially during extreme climate events during that time.
OK, last question. We’re living in a time when people are worried about rising CO2 levels. Obviously, not anything like you’re talking about [back then]–but is there any kind of scientific relevance, or even moral lesson to be drawn from this time?
Well, we’re looking at doubling CO2 concentrations now, during our lives. And it was a doubling or a tripling of CO2 in the past that looks like it was associated with these extinctions. Because we’re not starting at such a high temperature level as we were [then], the consequences of that doubling are hard to compare. But we do know, or think we know, that the time scale on which these changes occurred–the time scale over which the CO2 went up–[is] fully comparable to the human time scales, [on which] we are looking at for doubling of CO2 now. So there probably are very significant lessons to be learned about processes in the doubling of CO2. We have to get, however, the pattern, and the basic chronology and the basic history right first, before we try to learn great lessons about what lies ahead for us in the future.
DOI: 10.1126/science.1234204
