New Oxygen research; oxygen is needed (Introduction)

by David Turell , Wednesday, June 27, 2018, 18:57 (2131 days ago) @ David Turell

Studying layers from the Ediacaran/Cambrian interface shows the importance of oxygen levels:

https://phys.org/news/2018-06-mass-extinction-earth-animals.html

"Fossil records tell us that the first macroscopic animals appeared on Earth about 575 million years ago. Twenty-four million years later, the diversity of animals began to mysteriously decline, leading to Earth's first know mass extinction event.

"Scientists have argued for decades over what may have caused this mass extinction, during what is called the "Ediacaran-Cambrian transition." Some think that a steep decline in dissolved oxygen in the ocean was responsible. Others hypothesize that these early animals were progressively replaced by newly evolved animals.

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"But there is evidence to suggest that during the mass extinction event, there was a loss of dissolved oxygen in Earth's oceans, an effect called "marine anoxia."

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"To determine the levels of marine anoxia and its effects, the research team used a novel approach of combining geochemical data and the Earth's fossil record to precisely match evolutionary and environmental events.

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"To overcome this, the team pioneered a new and more efficient approach. Rock samples of marine limestone were collected in the Three Gorges Area (Hubei Province) of the People's Republic of China. This area is known for having some of the best examples in the world from the Ediacaran Period. The rock samples for this study were deposited in a shallow marine environmental between 551 and 541 million years ago, and hold a record of the marine environmental changes that occurred when they were deposited.

"Back at the lab, the team measured the uranium isotope variations in marine limestone and then then integrated the uranium isotope data and paleontological data from the same suite of rocks. Once the data were integrated, the team could clearly see that the episode of extensive marine anoxia coincided with the decline and the subsequent disappearance of early animals.

"'This may have been most severe marine anoxic event in the last 550 million years," says Zhang. "Mathematical modeling of our data suggests that almost the entire seafloor was overlain by anoxic waters during the end of the Ediacaran Period.'"

comment: oxygen when plentiful allows evolution, but does not drive it.