In the Triassic, about 240 million years ago, the triumph of the reptiles began. The first pterosaurs and sea dinosaurs developed and the ancestors of the dinosaurs grew to the most diverse group of terrestrial vertebrates. From them emerged the first real dinosaurs. When about 200 million people died from mass extinction, the dinosaurs were able to benefit: their relatives and predecessors were extinct, so that they could now occupy the vacant niches on land. Thus began the triumph of the dinosaurs. For a long time it was unclear what caused this mass extinction at the end of the Triassic. Initial indications, however, pointed to profound climate changes, combined with strong releases of carbon dioxide. Another indication is provided by the so-called Central Atlantic Magmen Province - a lava rock-covered area that once covered seven million square kilometers. Relics of these flood basalts can be found today mainly in North America and North Africa. Already a few years ago, dating revealed that these lava must have been ejected by huge, pulsating volcanic eruptions about 200 million years ago - and thus at the time of mass extinction. But how strong the impact of these outbreaks was and whether they were enough to explain the massive climate change was not known.
Now, however, Lawrence Percival of the University of Oxford and his colleagues may have provided the missing pieces of the puzzle for the primeval sunset scenario. For their study, they examined six sedimentary formations in Great Britain, Austria, Argentina, Greenland, Canada and Morocco, each created at the time of the mass extinction at the end of the Triassic period. In the rock samples, the researchers analyzed the mercury content. "Because volcanism is one of the great natural sources of mercury, " they explain. The heavy metal ejected with the volcanic gases remains gaseous for up to two years and can thus be distributed throughout the atmosphere before it precipitates and deposits on the ground. The mercury content in the sediment can therefore provide information on the intensity and global effects of volcanic eruptions.
It turned out that in five of the six sediment samples from the end of the Triassic, the researchers found strongly elevated mercury levels. "The onset of this flood of mercury occurred synchronously around the globe and coincided with the mass extinction at the end of the Triassic, " the scientists report. The more detailed analyzes revealed that the heavy metals had to be expelled and deposited in several pulses at that time. The outbreaks of the Central Atlantic Magmen province were therefore not only irregular in some places, as previously stated, but the activity of the entire volcanic area alternated cyclically. Three of the strongest pulses - and thus the strongest volcanic eruptions - occurred just before the end of the Triassic, as Percival and his colleagues report.
"These results strengthen the link between mass extinction at the end of the Triassic and episodes of volcanic activity at that time, " says Percival. "Such a volcanism must have disrupted the global environment for long periods of time and could have delayed the ecological recovery." Ad
- Lawrence Percival (University of Oxford) et al., Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073 / pnas.1705378114