Volcanoes had lower greenhouse gas emissions in Earth’s past

The Impact of Volcanoes on Earth’s Climate

The power of volcanoes to change Earth’s climate may not be as ancient as previously thought. Throughout our planet’s history, the climate has fluctuated between “icehouse” and “greenhouse” conditions, largely determined by the levels of greenhouse gases, such as carbon dioxide, in the atmosphere.

Volcanic arcs, the giant chains of erupting peaks in places like Japan, can play a part in this by releasing CO2 from Earth’s interior. Research led by Ben Mather at the University of Melbourne, Australia, suggests that volcanic arcs only became the dominant source of carbon emissions towards the end of the age of the dinosaurs, around 100 million years ago.

Mather explains that around 150 million years ago, phytoplankton with calcium carbonate scales emerged in the oceans. When these plankton die, they leave immense deposits of calcium carbonate on the deep-sea floor. As tectonic plates move and are recycled into Earth’s molten interior by subduction, these carbon deposits end up being pushed into the mantle.

“Most of the carbon from the plankton that leaves the subducting oceanic plate will get mixed into the molten interior, but a portion of that will get emitted via volcanic-arc volcanoes,” says Mather.

Before 150 million years ago, the material being released by volcanic arcs was relatively low in CO2 because of the absence of these scaly plankton. Mather and his colleagues have modeled the past half-billion years of plate tectonics and its role in the carbon cycle, revealing that through most of Earth’s history, carbon release occurred through rifting rather than volcanic arcs.

“Rifting is the process by which continents are torn apart on geological timescales and can happen on land or along mid-ocean ridges,” Mather explains. The emissions from volcanic arcs have significantly increased in the last 100 million years due to the new reservoir of carbon on the seafloor from phytoplankton, emitting two-thirds more carbon compared to 150 million years ago.

Currently, Earth is in a short warm period within a longer ice age that began 34 million years ago. The amount of carbon in volcanic arc eruptions has increased, but it is still less than what phytoplankton store on the seafloor and what gets pulled into Earth’s interior by tectonic movement.

Alan Collins at the University of Adelaide emphasizes the importance of modeling studies in understanding the impact of volcanism and tectonic activity on climate change over time. The composition of ocean sediments has evolved with different creatures, such as the dominance of calcium carbonate zooplankton.

Reference: Nature Communications Earth and Environment, DOI TK

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