In the last decade, there has been intense debate over whether the hyperthermal events mentioned above were caused by an increased Deccan volcanic activity, which emitted large amounts of gases into the atmosphere. The climatic changes caused by the eccentricity maxima and augmented by the Deccan volcanism occurred gradually at a scale of hundreds of thousands of years.
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Story Source: Materials provided by University of Barcelona. Contribution of orbital forcing and Deccan volcanism to global climatic and biotic changes across the Cretaceous-Paleogene boundary at Zumaia, Spain.
Geology , ; DOI: ScienceDaily, 20 September In total, this mass extinction event claimed three quarters of life on Earth. For now, two leading ideas are battling it out within the scientific community: Were dinosaurs victims of interplanetary violence, or more Earthly woes? One of the most well-known theories for the death of the dinosaurs is the Alvarez hypothesis, named after the father-and-son duo Luis and Walter Alvarez. In , these two scientists proposed the notion that a meteor the size of a mountain slammed into Earth 66 million years ago, filling the atmosphere with gas, dust, and debris that drastically altered the climate.
Iridium is relatively rare in Earth's crust but is more abundant in stony meteorites, which led the Alvarezs to conclude that the mass extinction was caused by an extraterrestrial object. At about 93 miles wide, the Chicxulub crater seems to be the right size and age to account for the dino die-off. In , scientists drilled a rock core inside the underwater part of Chicxulub , pulling up a sample stretching deep beneath the seabed. This rare peek inside the guts of the crater showed that the impact would have been powerful enough to send deadly amounts of vaporized rock and gases into the atmosphere, and that the effects would have persisted for years.
And in , paleontologists digging in North Dakota found a treasure trove of fossils extremely close to the K-Pg boundary , essentially capturing the remains of an entire ecosystem that existed shortly before the mass extinction. Tellingly, the fossil-bearing layers contain loads of tiny glass bits called tektites—likely blobs of melted rock kicked up by the impact that solidified in the atmosphere and then rained down over Earth. However, other scientists maintain that the evidence for a massive meteor impact event is inconclusive, and that the more likely culprit may be Earth itself.
Ancient lava flows in India known as the Deccan Traps also seem to match nicely in time with the end of the Cretaceous, with massive outpourings of lava spewing forth between 60 and 65 million years ago. Today, the resulting volcanic rock covers nearly , square miles in layers that are in places more than 6, feet thick. Proponents of this theory point to multiple clues that suggest volcanism is a better fit.
Other research has found evidence for mass die-offs much earlier than 66 million years ago, with some signs that dinosaurs in particular were already in a slow decline in the late Cretaceous. This all makes sense, supporters say, if ongoing volcanic eruptions were the root cause of the world-wide K-Pg extinctions.
Increasingly, scientists trying to unravel this prehistoric mystery are seeing room for a combination of these ideas. This nearly whole, deep-black skull belongs to the most complete specimen of Tyrannosaurus rex on display in Europe, an individual nicknamed Tristan Otto.
But that notion depends a lot on more precise dating of the Deccan Traps and the Chicxulub crater. Because nothosaurs may have had to come ashore to lay eggs, the eggs and hatchlings would have been vulnerable to Ticinosuchus. Yet once the hatchlings reached deeper waters, they were safe—for the moment. At the end of the Triassic, Earth warmed an average of between 5 and 11 degrees Fahrenheit, driven by a quadrupling of atmospheric CO 2 levels.
This was probably triggered by huge amounts of greenhouse gases from the Central Atlantic Magmatic Province, a large igneous province in central Pangaea, the supercontinent at the time. Remnants of those ancient lava flows are now split across eastern South America, eastern North America, and West Africa.
The Central Atlantic Magmatic Province was enormous. Its lava volume could cover the continental U. The uptick in CO 2 acidified the Triassic oceans, making it more difficult for marine creatures to build their shells from calcium carbonate. On land, the dominant vertebrates had been the crocodilians, which were bigger and far more diverse than they are today. Many of them died out. In their wake, the earliest dinosaurs—small, nimble creatures on the ecological periphery—rapidly diversified.
The Cretaceous-Paleogene extinction event is the most recent mass extinction and the only one definitively connected to a major asteroid impact. Some 76 percent of all species on the planet, including all nonavian dinosaurs , went extinct. One day about 66 million years ago, an asteroid roughly 7. The massive impact—which left a crater more than miles wide—flung huge volumes of dust, debris, and sulfur into the atmosphere, bringing on severe global cooling.
Wildfires ignited any land within miles of the impact, and a huge tsunami rippled outward from the impact. Overnight, the ecosystems that supported nonavian dinosaurs began to collapse.
Global warming fueled by volcanic eruptions at the Deccan Flats in India may have aggravated the event. Some scientists even argue that some of the Deccan Flats eruptions could have been triggered by the impact.
Earth is currently experiencing a biodiversity crisis. Recent estimates suggest that extinction threatens up to a million species of plants and animals , in large part because of human activities such as deforestation, hunting, and overfishing. Other serious threats include the spread of invasive species and diseases from human trade, as well as pollution and human-caused climate change.
Explore National Geographic magazine's special issue on extinction. Today, extinctions are occurring hundreds of times faster than they would naturally. If all species currently designated as critically endangered, endangered, or vulnerable go extinct in the next century, and if that rate of extinction continues without slowing down, we could approach the level of a mass extinction in as soon as to years.
Climate change presents a long-term threat. By total volume, these past volcanoes emitted far more than humans do today; the Siberian Traps released more than 1, times the CO 2 than humans did in from burning fossil fuels for energy. As mass extinctions show us, sudden climate change can be profoundly disruptive.
Well before hitting that grim marker, the damage would throw the ecosystems we call home into chaos, jeopardizing species around the world—including us. All rights reserved. Edaphosaurus A sail-backed edaphosaurus forages amid a Permian landscape in this artist's depiction. Fleeing Nothosaurs An artist's rendering shows hatchling nothosaurs heading for the safety of water as a hungry but terrestrial Ticinosuchus attacks near a lagoon in ancient Switzerland.
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