Explosive, Underwater Volcanoes Impacted 'Snowball Earth'
It turns out that explosive, underwater volcanoes may have been a major feature of "Snowball Earth." Scientists have taken a closer look at this period of time in Earth's history and have found that underwater volcanoes may have helped cover our planet's surface with ice.
Many aspects of the extreme glaciation that occurred 720 to 640 million years ago remain uncertain. However, researchers believe that the breakup of the supercontinent Rodinia resulted in increased river discharge into the ocean. This changed ocean chemistry and reduced atmospheric CO2 levels. This, in turn, increased global ice coverage and propelled Earth into severe icehouse conditions.
Because the land surface was largely covered in ice, continental weathering effectively ceased. This locked the planet into a "Snowball Earth" state until carbon dioxide released from ongoing volcanic activity warmed the atmosphere sufficiently to rapidly melt the ice cover. However, this model doesn't explain the global formation of hundreds of meters thick deposits known as "cap carbonates" in warm waters after Snowball Earth events.
"When volcanic material is deposited in the oceans it undergoes very rapid and profound chemical alteration that impacts the biogeochemistry of the oceans," said Tom Gernon, lead author of the new study, in a news release. "We find that many geological and geochemical phenomena associated with Snowball Earth are consistent with extensive submarine volcanism along shallow mid-ocean ridges."
During the breakup of Rodinia, tens of thousands of kilometers of mid-ocean ridge were formed over tens of millions of years. The lava erupted explosively in shallow waters producing large volumes of a glassy pyroclastic rock called hyaloclastite. As these deposits piled up on the sea floor, rapid chemical changes released massive amounts of calcium, magnesium and phosphorus into the ocean.
"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.
The findings are published in the journal Nature Geoscience.
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