Until then, life could not have evolved.
Did you know that Earth used to be really, really cold? About 720 to 640 million years ago, temperatures on the surface were a frigid -50 degrees Celsius (-58 degrees Fahrenheit) — a time period nicknamed “Snowball Earth” — brrr!
This was actually a very important time in Earth’s history, because when the ice started to melt, the ocean chemistry changed — allowing oxygen to form in the atmosphere and oceans and thus life to evolve.
What caused this change is one of the biggest mysteries for geoscientists, but now a new study out of the University of Southampton, published in Nature Geoscience, suggests that the transformation in ocean chemistry was caused by underwater volcanoes.
First of all, why did the ice finally start to melt? It turns out that the accumulation of millions of years’ worth of carbon dioxide (CO2) from volcanic activity on land led to enough atmospheric warming to start to melt the ice cover — fast! And since there was a layer of ice covering all of the oceans, CO2 was not absorbed by the water, so the melting continued.
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Experts say that the ending of Snowball Earth was the most extraordinary transition between icehouse to greenhouse that the planet has ever experienced.
The reason geoscientists know that this climate shift happened is because there are thick deposits, known as cap carbonates, that formed in the warm waters after Snowball Earth and are still visible in China and Namibia.
However, for these deposits to have formed, ocean water would have had to be very alkaline, meaning it could neutralize an acid. One way this alkalinity may have developed was through increased weathering of rocks on land during the meltdown, but if the melt was as rapid as geoscientists think, the rate of weathering necessary would have to have been orders of magnitude greater than today.
Hence, the mystery.
However, this new study suggests that widespread underwater volcanic activity, spanning thousands of kilometers along the mid-ocean ridge that formed during the breakup of Rodinia, lasted tens of millions of years in shallow waters, producing large amounts of glassy pyroclastic (volcanic) rock called hyaloclastite.
Lead author of the study Dr. Tom Gernon said in a press release, “When volcanic material is deposited in the oceans it undergoes very rapid and profound chemical alteration that impacts the biogeochemistry of the oceans. We find that many geological and geochemical phenomena associated with Snowball Earth are consistent with extensive submarine volcanism along shallow mid-ocean ridges.”
As the hyaloclastite continued to pile up on the ocean floor, chemical reactions between the rock and the ocean water led to large amounts of calcium, magnesium, silica and phosphorus being released.
Phosphorus is believed to have been the catalyst for the oxygenation of the atmosphere and oceans, and subsequently the evolution of single-celled organisms, according to Business Insider. Phosphorus is important in the creation of DNA and cell membranes, and underwater volcanoes would have prompted the production of multicellular organisms such as algae and cyanobacteria.
As a result of volcanic eruptions, these organisms — mostly made up of carbon, hydrogen and oxygen — were buried under the seafloor, capturing the carbon in the sediments. This led to an increase of free oxygen in the oceans and the atmosphere. The algae and cyanobacteria would also have produced and released oxygen through a process known as photosynthesis, which is crucial for animals to evolve.
“We calculated that, over the course of a Snowball glaciation, this chemical build-up is sufficient to explain the thick cap carbonates formed at the end of the Snowball event,” said Dr. Gernon.
Maybe geoscientists finally have the answer they have been searching for!