When the land that was now the Indian subcontinent entered Asia about 50 million years ago, a collision changed the shape of the continents, the landscape, the global climate and more. Now, a team of Princeton scientists has identified one more effect: the oxygen in the world's oceans has grown, and life conditions have changed.
"These results are different from what people have seen in the past," said Emma Kast, a graduate student in the leading natural sciences and society. science On 26 April. "The size of the reconstructed change surprised us."
Caste used microscopic tubes to create a record of ocean nitrogen over a period of 70 million years – shortly before the extinction of the dinosaurs – until 30 million years ago. This record is a tremendous contribution to global climate research, said John Higgins, professor of geological sciences at Princeton and co-author on paper.
"In our field there is documentation that you are looking at as a foundation that needs to be explained by any kind of hypothesis that wants to make biogeochemical connections," Higgins said. Fifty million years old rocks are not willing to give up their secrets, and I would definitely see her mother's record as one of those basic records. "From now on, people who want to deal with how the earth is Changed over the last 70 million years will have to deal with her mother's data. "
In addition to being the most abundant gas in the atmosphere, nitrogen is the key to life on Earth. "I'm studying nitrogen so I can learn the global environment," said Daniel Siegman, a professor at Duke University for geological and geophysical science at Princeton, and the senior author on paper. Sigman initiated the project with Higgins and Princeton postdoctoral researcher Daniel Stoller, who is now a professor of Earth and Planetary Sciences at the University of California at Berkeley.
Every organism on Earth requires "constant" nitrogen – sometimes called "bio-available nitrogen". Nitrogen accounts for 78% of our planet's atmosphere, but only a few organisms can "fix" it by turning the gas into a biologically useful form. In the oceans, cyanobacteria in internal water fix nitrogen for life and other ocean. As cyanobacteria and other creatures die and sink downward, they fall apart.
Nitrogen has two stable isotopes, 15N and 14N. In oxygen-free water, decomposition uses "fixed" nitrogen. This happens with a slight preference for easier nitrogen isotope, 14N, so the ratio of 15N to 14N of the ocean reflects its oxygen levels.
This ratio is combined with tiny sea creatures called Lorimifera during their lifetime, and then kept in their shells when they die. By analyzing their fossils – collected by the Atlantic Ocean, the North Pacific Ocean, and the South Atlantic – Kast and its colleagues were able to restore the ratio of 15N to 14N of the ancient ocean, thus detecting past changes in oxygen levels .
Oxygen controls the distribution of marine organisms, with poor water and oxygen being bad for most ocean life. Many climatic warming events caused a reduction in ocean oxygen that restricted the habitats of marine creatures, ranging from microscopic plankton to fish and whales feeding them. Scientists trying to predict the impact of current and future global warming have warned that low oxygen levels in the ocean could destroy marine ecosystems, including important fish populations.
When researchers assembled the unprecedented geological record of ocean nitrogen, they found that at 10 million years after extinct dinosaurs, the ratio of 15N to 14N was high, suggesting that ocean oxygen levels were low. They first thought that the warm climate of time is responsible, as oxygen is less soluble in hot water. But the timing told a different story: the change in ocean oxygen high occurred around 55 million years, during a period of warm climate continuously.
"Contrary to our first expectations, the global climate was not the main cause of this change in ocean oxygen and nitrogen cycling," Kast said. Is Hashem more likely? Table tectonics. The clash between India and Asia – dubbed the "collision that changed the world" by legendary geologists Wally Brocker, one of the founders of modern climate research – closed an ancient sea called Tetis that disturbed land shelves and their connections with the open ocean.
"For millions of years, tectonic changes have the potential to have a massive impact on the ocean cycle," said Sigman. But that does not mean climate change can be discounted, he added. "On the schedules of years to thousands of years, the climate on top."