March 22, 2013
Megavolcanoes Led To End-Triassic Extinction Allowing Dinosaurs To Evolve
WATCH VIDEO: [Drilling Into The Jurassic In New Jersey]
Lawrence LeBlond for redOrbit.com - Your Universe Online
An examination of evidence across three continents has given scientists an indication that half of the Earth´s species disappeared 200 million years ago due to gigantic volcanic eruptions. They suggest that the eruptions may have caused climate changes so sudden that many creatures were unable to adapt, opening an avenue for dinosaurs to evolve and dominate the planet.
In recent times, science has suggested that at least five known die-offs were caused in part by mega-volcanic eruptions followed by global climate change. However, many of these events have not been dated accurately. The new study, however, has provided the tightest link yet to a megavolcanic event, precisely dating the End-Triassic Extinction (ETE) event to 201,564,000 years ago, exactly at the same time a massive outpouring of lava occurred.
"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," said coauthor Paul Olsen, a geologist at Columbia University's Lamont-Doherty Earth Observatory (LDEO) who has been investigating the ETE boundary since the 1970s.
The study ties together several lines of evidence along with newly devised techniques for dating rocks.
Terrence Blackburn, lead author of the paper who originally worked on the study while at MIT (now at Carnegie Institution), used the decay of uranium isotopes to pull exact dates from basalt, a type of rock left by eruptions. The basalts dated in the study all came from the Central Atlantic Magmatic Province (CAMP), a series of giant eruptions that started around 201 million years ago when the world was one large supercontinent.
The mega eruptions spewed 2.5 million cubic miles of lava over four sudden events over a 600,000-year period. The eruptions led to a rift that evolved into the Atlantic Ocean, and evidence of CAMP lavas can be found in North and South America, and North Africa. More specifically, the researchers pulled basalt samples from Nova Scotia, Morocco and the NYC suburbs.
Previous studies have suggested a link between the CAMP eruptions and the extinction, but their dating models had a margin of error of 1 to 3 million years. The new study has narrowed down that margin to less than a few thousand years, the most precise dating yet for such a prehistoric event.
PIECING TOGETHER THE EVIDENCE
Blackburn and his colleagues showed that the eruption in Morocco was the earliest, with the Nova Scotia eruption coming 3,000 years later and the NYC/New Jersey eruption 13,000 years later. Sediments below that time contain fossils characteristic of the Triassic era; in the sediments above the basalt, those fossils disappear. Creatures that vanished during the ETE included eel-like fish called conodonts, early crocodilians, tree lizards and various broad-leaf plants.
Another piece of evidence that strengthens Blackburn and colleagues´ findings is that a layer of sediment just before the ETE contains mineral grains providing evidence of one of the planet´s many periodic reversals of magnetic polarity. This particular reversal, called E23r, is consistently located just below the ETE boundary, making it a convenient marker.
Study coauthor Dennis Kent, a paleomagnetism expert at the LDEO, said these same layers were found everywhere the team had searched so far, adding that the eruptions “had to be a hell of an event.”
Blackburn and his team also uncovered a third piece of chronological evidence: the sedimentary layers themselves. Olsen has 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 beds on a fairly steady 20,000-year schedule. Most scientists have accepted this idea pertaining to recent history, but many have doubted it could be applied for dates farther back.
By correlating the precisely dated basalts with the surrounding sedimentary layers, the new study shows precession operated pretty much the same way then, allowing for precise dating of sediments holding fossils to within 20,000 years, said Olsen.
Olsen has meticulously cataloged the layers around the ETE, finding that the initial phase of the extinction occurred in a single layer — meaning the event took no more than 20,000 years. Although, he noted, “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."
Previous research has suggested that giant eruptions would have sent sulfurous particles into the atmosphere that would have darkened skies and led to multi-year winters, perhaps freezing out many animals. Another study showed that each eruption would have doubled the carbon dioxide concentration in the air, choking out life over time. Following cold spells, warming effects of the greenhouse gas would have lasted for millennia, leading to further extinction in animals not able to handle too much heat.
Fossil evidence shows that heat-sensitive plants around the time of the ETE suffered, and CO2 levels caused chemical reactions that made the seas more acidic than they are today, causing the marine ecosystem to collapse.
There is also some evidence that a large meteorite hit the earth around the time of the ETE — although most scientists discount that theory with some certainty. However, while the ETE led to the evolution explosion for dinosaurs, their fate was sealed 65 million years ago when the Chicxulub meteor caused the CPE event, opening the door for the evolution and dominance of mammals, including humans.
There is some evidence as well that dinosaurs were already on their way out due to increased volcanism, with the meteor impact delivering the final blow.
The End-Triassic was the fourth known global die-off; the CPE event when dinosaurs vanished was the fifth. Now, there are those who say that the world is on the cusp of a sixth extinction — this one due to man.
The burgeoning population, industrial activity and exploitation of natural resources (which includes the burning of fossil fuels) are pushing many species off the map. Industrial emissions has had the largest effect, raising atmospheric CO2 levels by more than 40 percent over the past 200 years — a pace equal to, or even faster than, the End-Triassic.
Rising temperatures are also altering ecosystems and CO2 levels are on the rise in oceans, leading to increased acidification.
"In some ways, the End Triassic Extinction is analogous to today," Blackburn said in a statement. "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."
The study is published in the latest issue of the journal Science.