But most life is concentrated in shallow water, in places like reefs. In English geologists Paul Wignall and Richard Twitchett of the University of Leeds reported the first evidence of oxygen depletion, or anoxia, in rocks that formed under shallow water at the time of the extinction. Pollution sometimes turns waters anoxic today in regions that lack good circulation. Local die-offs of marine life can result. But Wignall suspects that the entire ocean may have stagnated in Permian times.
What could still the currents that oxygenate the ocean? Perhaps a lack of ice caps during the late Permian led to the stagnation. Normally temperature differences between polar and equatorial waters create convective currents.
Without those currents, anoxic water could have built up, spilling into shallow water as sea levels rose and smothering marine life.
Permian oceans also might have been poisoned with CO2, according to Andrew Knoll, a paleobiologist at Harvard. Oceanic bacteria eat organic matter, producing bicarbonate as a digestive by-product.
Without currents, the load of bicarbonate could have grown in the deep ocean. Knoll thinks something big—he's not sure what—disturbed the seas. Bicarbonate-laden water rose from below, he suggests. As it did, it depressurized. Dissolved bicarbonate was released as CO2, making the seas bubble at times like a glass of soda.
The crisis for marine animals would have started when toxic levels of CO2 entered the shallows. Fish would have grown lethargic and slowly fallen asleep. Another suspect—a deadly epoch of volcanic eruptions—left a million-square-mile 2. Below the town of Norilsk lies a two-and-a-half-mile-thick four-kilometer-thick pile of lava, overgrown by conifers.
Geologists call this vast lava field the Siberian Traps. It wasn't produced by one volcano. For decades scientists have known the Siberian Traps were formed around the time of the Permian extinction.
Could the greatest extinction be related to the greatest volcanic eruptions? Renne, an expert at determining the ages of rocks, has been trying to work out the timing of the events. His lab is filled with machines—tangles of high-voltage cables, vacuum lines, and stainless steel—that date rocks by measuring the decay of radioactive isotopes within them.
He has determined the two events occurred within , years of each other. Renne doubts that's a coincidence. But the Siberian Traps volcanoes didn't cause the extinction by swamping the world with lava. As volcanic gases poured into the skies, they would have generated acid rain, and sulfate molecules would have blocked sunlight and cooled the planet.
Glaciation would have reduced the volume of water in the ocean, storing it as ice. Sea level would have dropped, killing marine life in the shallows and severely reducing diversity.
Lowering sea level can also release the ocean's methane, which, combined with CO2 from the eruptions and decaying organic matter, would likely produce greenhouse conditions. Imagine a Laki erupting every year for hundreds of thousands of years.
Each scientist I met left me thinking that he or she was a clue or two away from solving the crime. But as Doug Erwin of the Smithsonian cautioned me, "the truth is sometimes untidy. Twelve different killers conspired to slay the victim.
Erwin suspects there may have been multiple killers at the end of the Permian. Maybe everything—eruptions, an impact, anoxia—went wrong at once. Could it happen again?
A hundred million years from now? But as their methods for dating the disappearance of species has improved, estimates of its duration have shrunk from millions of years to between 8, and , years. That's a blink of the eye in geological terms. Becker's evidence, however, is more direct and persuasive:.
Above: The carbon atoms in a fullerene molecule are arranged in a spherical pattern similar to a geodesic dome. Geodesic domes were invented by Buckminster Fuller, hence the name of the molecules. This shape allows the fullerenes to trap gases inside. Image courtesy Luann Becker. Becker's team had previously found such gas-bearing buckyballs in rock layers associated with two known impact events: the 65 million-year-old Cretaceous-Tertiary impact and the 1.
They also found fullerenes containing similar gases in some meteorites. Taken together, these clues make a compelling case that a space rock struck the Earth at the time of the Great Dying. But was an asteroid the killer, or merely an accomplice? Many scientists believe that life was already struggling when the putative space rock arrived. Our planet was in the throes of severe volcanism.
In a region that is now called Siberia, 1. For comparison, Mt. By the Late Triassic there was a shift in dominance between the mammal-like reptiles and the archosaurs.
There are various theories as to what may have caused this, such as competition in a climate that was becoming steadily warmer and dryer or evolutionary stagnation. It seems that archosaurs were better able to fill the empty niches left following the extinction of some of the synapsid linages.
Drepanosaurs were truely strange animals, and even today no one is quite sure where exactly they fit on the evolutionary tree. The neck of Tanystropheus was extraordinarily long, equal to the length of its body and tail combined. Others included the incredibly long-necked Tanystropheus and, potentially, the bizarre chameleon-like drepanosaurs, which had a claw on the end of their tails.
Another successful group was the phytosaurs. These animals looked quite crocodilian, but were from a different branch of the archosaurian tree. The lineage that would give rise to the crocodiles was instead represented in the Triassic by much smaller, more gracile animals.
It was around million years ago that the first dinosaurs appear in the fossil record. These dinosaurs were small, bipedal creatures that would have darted across the variable landscape.
The environment during the Triassic was as varied as it is today, with large swathes of forests, dry deserts and open prairies. There would likely have been an extremely arid interior, but also some very moist and wet temperate and tropical environments too. While reptiles were already dominating the oceans and the land, they also took the skies.
By million years ago, the first pterosaurs appeared, making them the earliest vertebrates to evolve powered flight. They would eventually evolve into extraordinary animals with a wingspan of over 15 metres, but the first pterosaurs were much more modest in size with long jaws and tails.
Even though the archosaurs had managed to usurp the synapsids, some still clung on. By million years ago, one branch gave rise to the mammaliaformes, which were likely small, nocturnal insectivores.
It is from this group that the mammals would later emerge. While the non-dinosaurian archosaurs continued to dominate most environments, the dinosaurs rapidly started to diversify. Not long after they first appeared, the dinosaurs may have already diverged into two main groups. These were the Saurischia, which includes the sauropods, and the Ornithoscelida, which includes the theropods and ornithischians.
By the end of the Triassic, some of these early dinosaurs were impressive in size. A few of the first relatives of sauropods, such as Riojasaurus and Lessemsaurus , had already reached over nine metres in length. The climate started to change so that by Journal Reference : Michael R. Global nickel anomaly links Siberian Traps eruptions and the latest Permian mass extinction.
Scientific Reports , ; 7 1 DOI: ScienceDaily, 2 October New York University. Siberian volcanic eruptions caused extinction million years ago, new evidence shows.
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