Northern New Jersey, southern Connecticut and environs are not necessarily where one would expect to explore the onetime extinction of much life on earth, and subsequent rise of dinosaurs. But it turns out to be a pretty good place to start. Underlying the exurbs are geological formations left by three giant episodes of volcanism starting around 200 million years ago, and intervening layers of sediments that built up in the interims between massive lava flows. They are part of the so-called Central Atlantic Magmatic Province, whose remains are now spread over four continents. But only here have scientists found layers that are exquisitely preserved and precisely dated, and that makes them ideal for studying what was happening to life on earth in those times.
In a new paper in the journal Science, three scientists including geologist Dennis Kent of Lamont-Doherty Earth Observatory, have found that the concentration of carbon dioxide in the air doubled after each episode of volcanism. All volcanoes spew CO2, but these eruptions, lasting 20,000 years each and dwarfing anything seen or imagined in human times, must have spewed a lot. Some scientists think the outgassing brought about the Triassic-Jurassic extinction, a sudden destruction of many species 200 million years ago that led to the rise and dominance of dinosaurs. This is the first time anyone has shown clearly that the cause could indeed have been massive CO2 releases fromvolcanism, which presumably would have warmed the planet, thrown the environment out of kilter, and cleared the way for the original Jurassic Park.
Morgan Schaller (a grad student of Kent’s at Rutgers University, and lead author), Kent and Jim Wright made the findings using deep cores drilled in the region in the 1980s and 1990s. The cores penetrated three 150-t0-300-foot lava sheets,each separated by some 600 feet of sediments that built up in the 200,000 or so years between each volcanic episode. Carbon isotopes in the sediments showed skyrocketing CO2 levels in the air following the eruptions. The CO2 levels gradually decayed, only to be renewed with the next eruption. “You see these big eruptions throughout earth’s history. But it’s always been unclear what they can do to the atmosphere,” Schaller said in a Rutgers news release. “It turns out, they may do a lot.”
This is hardly the last word on the Triassic-Jurassic extinction. Exactly how the shift in species fit in with the volcanism over time and space, and whether other factors were involved is not yet clear. Kent’s next stop is a May expedition with Lamont paleontologist Paul Olsen to seaside cliffs along the UK and Northern Ireland, where they will chisel and drill out rock samples from the time of the extinction. With these, they hope to help test an alternate hypothesis: that it was instead (or maybe additionally) linked to a catastrophic meteorite impact that either set off the eruptions, or just wiped out things on its own.