Fossil records tell us that the first macroscopic animals appeared on Earth 575 million years ago. Twenty-four million years later, the variety of animals mysteriously began to decline, leading to the Earth's first mass extinction event.
Scientists have been debating for decades what might have caused this mass extinction during the so-called "Ediacara" Cambrian transition. "Some believe that a large drop in dissolved oxygen in the ocean was responsible, while others hypothesize that these early animals have been gradually replaced by newly developed animals.
The exact cause has not been revealed, in part, because so little is known about the chemistry of the oceans long ago
Scientists at Arizona State University, funded by NASA and the National Science Foundation, help unravel this mystery and understand why this extinction event happened, what it did tell us about our origins and how the world came into existence as we know it.The study, published in Science Advances, was led by Feifei Zhang, a student at the ASU School of Earth and Space Exploration, led by the Faculty member Ariel Anbar and scientific assistant Stephen Romaniello.
The meaning of oxygen
He In most oceans in the world, there is an abundance of oxygen, an important part of life. However, there is evidence that during the mass extinction the dissolved oxygen in the oceans has been lost, an effect called "marine anoxia".
To better understand the mass extinction, the research team focused on studying this effect. They wanted to see not only how strong the ocean was when the animals began to sink, but also whether marine anoxia contributed to the decline and eventually extinction of the early animals.
Integrating Geochemistry and Earth's Fossils [1
Typically, scientists determine the anoxia of the oceans abound in pyrite, commonly known as "fool's gold," and other elements and minerals in ancient mudrocks. But Mud Rocks only give clues as to what might have happened in a single location. Scientists need to examine dozens of sites around the world to derive the big picture from mud.
To overcome this, the team pioneered a new and more efficient approach. Marine limestone rock samples were collected in Three Gorges (Hubei Province) of the People's Republic of China. This area is known for some of the best specimens of the Ediacaran period. The rock samples for this study were deposited in a shallow marine environment between 551 and 541 million years ago and document the changes in the marine environment that occurred during their deposition.
Back in the lab, the team measured uranium isotope variations in marine limestone and then integrated the uranium isotope data and paleontological data from the same group of rocks. Once the data was integrated, the team could clearly see that the episode of extensive marine anoxia coincided with the decline and subsequent disappearance of early animals.
"This may have been the worst marine anoxic event in the last 550 million years," Zhang said, "mathematical modeling of our data suggests that almost the entire seabed at the end of the Ediacaran period was overshadowed by anoxic waters."
Is there a mass extinction in our future?
While our oceans are currently undergoing a Increases in Oxygen Enrichment in the Oceans Attributed to Climate Change by Scientists Advances in the study of ancient marine anoxia, such as this, can help us to understand and predict the future.
"The past is our best laboratory for the future "Co-author Anbar says," It's sobering to see how often the mass extinctions of the past preceded an increase in the anoxia of the ocean, and much of what we have learned about climate change l do not understand is a big cause for concern.
Arizona State University
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Why Life First Got Big on Earth
Cambridge UK (SPX) June 26, 2018
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