An Earth-bound asteroid brought a swift end to the time of the dinosaurs. But that impact may have had help in its deadly outcome, a new study concludes. Volcanic activity began in what is now India prior to the collision. It then continued on, long after the impact, the new study finds. Those eruptions may have spoiled the climate for dinos and other forms of life, the team of scientists now argues.
The Deccan Traps is a rock formation in western India. As large as Spain, it formed through a long period of violent eruptions. Some of its peaks stand 3 kilometers (nearly 2 miles) high. New analyses show that the Deccan eruptions began 250,000 years before Chicxulub (CHEEK-shuh-loob) — the dino-killing asteroid — slammed into Earth. And those eruptions continued to spew rock and debris for another half-million years after the collision, the new calculations show. Those new dates appear in a report published December 11 in Science.
“For the last 30 years it has been basically ruled as the given truth that Chicxulub caused the [dinosaurs’] extinction,” Gerta Keller told Science News. Keller is a paleontologist, or scientist who studies fossils, at Princeton University in New Jersey. She says her team now finds “that maybe Chicxulub was not the main cause.” Climate change caused by the eruption may have helped send the dinosaurs into extinction.
Not all scientists agree. David Fastovsky is among the skeptics. The fossil record points to a single event — that asteroid impact — as a trigger for the mass extinction, says this paleontologist at the University of Rhode Island in Kingston. A long period of climate change does not match the story told in the rocks, he argues.
“Those of us who are ‘impactors’ have to keep an open mind to other possibilities,” he told Science News. An impactor is someone who supports the idea that an asteroid caused the die-off. “But,” Fastovsky maintains, “the question that needs to be answered is: If the asteroid is good enough, why do you need this?”
Dinosaurs weren’t the only living things to perish some 66 million years ago. Their demise was just one part of a massive die-off. About 60 percent of all plants and animals on Earth disappeared forever at the same time. The event is known as a mass extinction. (A few species of birdlike dinosaurs, the ancestors of modern chickens and other birds, survived.) Also about the same time, the Deccan volcanoes began to spew lava, gas and rock.
Scientists know of five mass extinctions in history. Three coincided with major volcanic activity — including the dino die-off, we now know. As gas and debris from the volcanoes filled the air, the atmosphere darkened and cooled. This changed Earth’s global climate. And during those periods, many plants and animals found it hard to survive.
Scientists had previously suggested that volcanoes might have contributed to the dinosaurs’ extinction. But they couldn’t be sure. Most importantly, they didn’t know if the Deccan eruptions occurred at the same time as the dino disappearances.
To estimate the dates of the Deccan eruptions, Keller and her coworkers studied crystals of zircon trapped in layers of lava. During an eruption, the crystals formed inside pools of magma, or hot liquid rock. The zircon absorbs uranium, a radioactive substance. Over time, some of that uranium changes into lead through a process known as radioactive decay.
“The crystals are like little time capsules,” Blair Schoene told Science News. A geologist at Princeton University, he led the study. His group compared the ratio of uranium to lead in the crystals to estimate their age. These scientists now estimate that the Deccan eruptions produced 80 to 90 percent of their ejected rock during a 750,000-year period. This dating of the eruptions is more precise than ever before.
Geoscientist Paul Renne works at the University of California, Berkeley. He says scientists who study the dinosaur die-off should consider both the Deccan eruptions and the asteroid as likely contributors. The deadly double blow, he says, points to an important unanswered question: “If there hadn’t been an asteroid impact, would there have been a mass extinction anyway?”
asteroid A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
Chicxulub The name given to a meteorite (landed asteroid) that crashed into Earth around 66 million years ago. It left a crater more than 180 kilometers (110 miles) wide near the town of Chicxulub in what is now Mexico. The collision released an immense amount of energy — equivalent to billions of atom bombs the size of those dropped on Japan during World War II. This event changed the planet’s climate and is widely believed to have triggered a mass extinction of species — including the end of the dinosaurs.
climate The weather conditions prevailing in an area in general or over a long period.
climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
crystal A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.
debris Scattered fragments, typically of trash or of something that has been destroyed. Space debris includes the wreckage of defunct satellites and spacecraft.
Deccan Traps A geologic formation created during a 750,000-year period as an enormous system of volcanoes erupted more or less continuously in what is now India.
extinct An adjective that describes a species for which there are no living members.
extinction The permanent loss of a species, family or larger group of organisms.
lava Molten rock that comes up from the mantle, through Earth’s crust, and out of a volcano.
magma The molten rock that resides under Earth’s crust. When it erupts from a volcano, this material is referred to as lava.
mass extinctions Any of several periods in the distant geological past when many — if not most — of the larger animals on Earth disappeared forever. One that occurred as the Permian period gave way to the Triassic, sometimes called the Great Dying, led to the loss of most fish species. Our planet has experienced five known mass extinctions. In each case, an estimated 75 percent of the world’s major species died off in a short time period, typically defined as 2 million years or less.
meteorite A lump of rock or metal from space that has entered Earth’s atmosphere. In space it is known as a meteoroid. When you see it in the sky it is a meteor. And when it hits the ground it is called a meteorite.
paleontologist A scientist who specializes in studying fossils, the remains of ancient organisms.
radioactive An adjective that describes unstable elements, such as certain forms (isotopes) of uranium and plutonium. Such elements are said to be unstable because their nucleus sheds energy that is carried away by photons and/or and often one or more subatomic particles. This emission of energy is by a process known as radioactive decay.
radioactive decay A process by which an element is converted into a lighter element through the shedding of subatomic particles (and energy).
uranium The largest naturally occurring element known. It’s called element 92, which refers to the number of protons in its nucleus. One form (isotope) is radioactive, which means it decays into smaller particles. The other form is stable.
volcano A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.
zircon A gemstone that contains traces of the radioactive element uranium. It develops as a crystal that forms as magma (from deep inside Earth) begins to cool. Some of the oldest minerals surviving on the planet are crystals of zircon that are at least 4.2 billion years old. For perspective, Earth is only 4.56 billion years old.
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Original Journal Source: B. Schoene et al. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science. Published online Dec. 11, 2014. doi: 10.1126/science.aaa0118.