Privileged planet: influence of oxygen levels (Introduction)

by David Turell , Monday, July 08, 2024, 15:57 (139 days ago) @ David Turell

Did oxygen levels drive evolutionary complexity?:

https://www.sciencealert.com/life-only-needed-a-small-amount-of-oxygen-to-explode-scien...

"Now, new research scouring the globe for geological data suggests oxygen didn't flood the atmosphere and oceans a little over half a billion years ago, so much slowly dissolve into shallow basins and oceanic shelves.

"That doesn't mean oxygen played no role in kickstarting the burst of biodiversification that gave rise to all the weird, wacky and wild creatures we see today.

"'Cambrian animals likely did not require as much oxygen as scientists used to believe," says Erik Sperling, a geobiologist at Stanford University and senior author of the new study.

"'We found minor increases in oxygenation" – in sedimentary rocks formed on the bottom of ancient oceans – "that are at the correct magnitude to drive big changes in ecology."

"Without enough oxygen, single-celled organisms and other small creatures eking out an existence before the Cambrian explosion wouldn't have been able to grow much bigger and expand their body plans, scientists have reasoned.

***

"Their analysis of two trace metals, molybdenum and uranium, both indicators of global ocean oxygen levels, along with biogeochemical models of oxygen flows between the oceans and atmosphere, suggest that oxygen levels in the deep ocean didn't reach modern levels until 140 million years after the Cambrian explosion, in the Devonian period.

"'From a global perspective, we didn't see the full oxygenation of the oceans to near modern levels until about 400 million years ago, around the time that we see the appearance of large forests on land," explains Richard Stockey, a palaeobiologist at the University of Southampton, who led the study.

***

"The team's findings expand on the results of a 2017 study, which found shallow seas became oxygenated first, but atmospheric oxygen didn't reach modern levels until some 50-100 million years after the Cambrian explosion, during the Ordovician period that followed.

"However, other recent research has found that oxygen levels started rising in early Ediacaran period some 640–600 million years ago, in the first of three successive oxygen pulses that coincided with important evolutionary leaps in the lead-up to the Cambrian explosion.

"Meanwhile, other researchers contest that oxygen levels throughout deep time have been extremely variable so it's hard to say what effect they had on blossoming biodiversity."

Comment: Be clear in your thinking that oxygen doesn't cause anything. It's availability for use is the issue.