Cosmology: snowball Earth possible cause (Introduction)

by David Turell , Thursday, July 13, 2023, 17:05 (289 days ago) @ David Turell

New research on an old theory:

https://www.science.org/content/article/massive-lava-outburst-may-have-led-snowball-ear...

"About 717 million years ago, a climate catastrophe struck the planet, as temperatures plunged and glaciers enveloped the globe. The cause of this “Snowball Earth” episode has been mysterious, but it took place around the same time as a massive outburst of volcanism. Many researchers thought there might be a connection. But the timing was uncertain.

"Now, more precise dates, reported last month in Earth and Planetary Science Letters (EPSL) and in November 2022 in Science Advances, show the eruptions preceded the Snowball Earth event by 1 million to 2 million years. The lag points to a particular way the fire could have triggered the ice: through a chemical alteration of the fresh volcanic rocks known as weathering, which sucks carbon dioxide (CO2) from the atmosphere, turning down the planetary thermostat. The studies highlight the power of weathering as a key driver behind shifts in Earth’s climate, and how components of the planet as disparate as rocks and the atmosphere are inextricably linked, says EPSL study co-author Galen Halverson, a sedimentary geologist at McGill University. “Nothing can be understood in isolation.”

"Geoscientists debating the cause of the so-called Sturtian glaciation, which lasted 57 million years, have pointed to a number of possibilities—meteorite strikes, biologic activity, shifts in Earth’s orbit, and more. But recent studies have zeroed in on one of the largest volcanic outbursts ever, preserved today across northern Canada in what’s called the Franklin large igneous province (LIP). The eruptions spewed lava across an area at least the size of Argentina—and perhaps bigger than China.

"Volcanism can trigger cooling in two main ways. In one, eruptions release sulfur-rich gases, which form aerosols that block sunlight and cool the planet. A section of the Franklin lava likely even burst through rocks full of sulfur-rich minerals that could have supercharged the plumes. The other mechanism is weathering. Lava rocks are particularly susceptible to the reactions, in which CO2 in rainwater reacts with the rocks, ultimately forming minerals that precipitate in the ocean.

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"By measuring the ratios of trace amounts of uranium and lead trapped in tiny crystals of the mineral zircon—and knowing how fast uranium decays to lead—the teams discovered that the Franklin LIP formed in just 2 million years or so, much faster than most previous estimates. And the primary pulse of volcanism happened 1 million to 2 million years before Snowball Earth, which has been dated through analysis of rocks scoured up by glaciers and eventually deposited in the ocean.

"That’s exactly the sort of time frame required for weathering to cause the cooling. “They’re just stunning the extent to which [the dates] all line up,” Halverson says. Additional analysis by Pu and her colleagues suggest the Franklin LIP formed a broad volcanic highland that would have been battered by wind and water, speeding up the weathering.

"Pu says other factors may have dialed up the weathering enough to cause a Snowball Earth event. For starters, all of Earth’s landmasses at the time were located near the equator, where temperatures were warm and rain frequently pelted the surface. The floods of lava also emerged during the breakup of the Rodinia supercontinent, which exposed fresh rocky surfaces to weathering and may have already begun to cool the global climate. And Gumsley says other large eruptions probably took place at this time in Siberia, China, Africa, and Antarctica, adding to the overall weathering effect.

"Case closed? Not for Harvard University geologist emeritus Paul Hoffman, a coauthor on the Science Advances study who led much of the early work on Snowball Earth. Even if the timing of the Franklin LIP has improved, that of the global glaciation remains slightly uncertain, he says. Forming the ice-scoured rock that marks the start of the episode requires the flow of thick ice at sea level, a process that may not have started until several hundred thousand years after the oceans froze over.

"Other Snowball periods remain mysterious. Some 650 million years ago, not long after the Sturtian glaciation, the planet plunged into another deep freeze—but no volcanic outburst preceded it, notes Linda Sohl, a paleoclimatologist at Columbia University who was not part of the study teams. Still, Halverson says weathering may have been a key factor then, too, because all the scouring by glaciers during the earlier Snowball would have exposed fresh rock.

"For the Sturtian glaciation at least, the case for a weathering trigger has grown, Sohl says. “In the very least, a revisit with weathering models seems in order,” she says. “The snowball glaciations are such fascinating events that are going to keep all of us quite busy for years to come.'”

Comment: previous entries described how life survived these periods.