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. But modelling research led by at the University of Melbourne, Australia, suggests they only became the dominant source of carbon emissions towards the end of the age of the dinosaurs, around 100 million years ago.

This is because 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, says Mather.

As tectonic plates move and are recycled into Earth’s molten interior by slipping under each other, a process known as subduction, these huge reservoirs of stored carbon 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.

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However, 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, says Mather.

He and his colleagues have modelled the past half-billion years of plate tectonics and its role in the carbon cycle. They found that through most of Earth’s history, much of the carbon locked inside the planet was released along fissures in Earth’s crust in a process called rifting, not by volcanic arcs.

Rifting is the process by which continents are torn apart on geological timescales and can happen on land, such as at the East African Rift, or along mid-ocean ridges.

“When tectonic plates are being spread apart, essentially, what you’re doing is ‘unroofing’ some of the molten interior of the Earth,” says Mather. “When that happens, you get new crust being formed at mid-ocean ridges and emission of carbon.”

The amount of carbon released into the atmosphere from continental rifts and mid-ocean ridges is a product of the length of the rift and how fast they pull apart, says Mather, but the proportion of carbon released previously stayed comparatively steady. “But the emissions from volcanic arcs have significantly increased in the last 100 million years thanks to this new reservoir of carbon on the seafloor from these plankton calcium carbonate suppliers,” he says. “Compared to 150 million years ago, volcanic arcs now emit two-thirds more carbon.”

Earth is currently in a short, warm period known as an interglacial within a much longer ice age that began 34 million years ago. One factor contributing to the ongoing cool spell is that these phytoplankton take so much carbon out of the ocean and lock it into the sea floor. While the amount of carbon in volcanic arc eruptions has increased, it is still less than what the phytoplankton store on the sea floor and what gets pulled into Earth’s interior by tectonic movement.

at the University of Adelaide, Australia, says modelling work such as this study is vital to understanding how the impact of volcanism and tectonic activity on the climate has changed through time.

“The composition of ocean sediments has changed as different creatures evolve that use different elements in their composition, such as the evolution and progressive dominance of calcium carbonate zooplankton,” says Collins.

Journal reference: Nature Communications Earth and Environment, DOI TK

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A drying climate in East Africa reduced the amount of water in Kenya’s Lake Turkana over thousands of years, which unleashed earthquakes and volcanoes from underneath it. This hazard of climate change could eventually affect other bodies of water around the world as rain and drought patterns shift.

Lake Turkana is often called the cradle of humanity, as fossils up to 4.2 million years old have been found there from at least half a dozen hominin species, some of which appear to have co-existed. As the lake shrank over recent millennia, those human ancestors would have had to contend not only with a drying climate, but also with greater seismic activity.

“We postulate that there would have been more frequent earthquakes and more frequent volcanic eruptions during these time intervals,” says at Syracuse University in New York. “It would have compounded the already difficult conditions that can be observed today in that area.”

Lake Turkana is located between Kenya and Ethiopia in the Great Rift valley, a place where the continental plate is slowly splitting and spreading apart. It is the largest desert lake in the world, a body of greenish, salty water ringed by sandy shrublands and windy outcrops. But nine millennia ago, the lake was even bigger and surrounded by lush grasslands and pockets of forest.

Between 4000 and 6000 years ago, the climate became drier and the water levels in the lake dropped by 100 to 150 metres. Lower water levels create less pressure on the lakebed below, which can impact seismic activity. To determine the effects of this climate change, Scholz and his colleagues identified certain sediment layers corresponding to different time periods in cores that had previously been taken from the lakebed.

From a boat, they then performed sonar imaging at 27 faults on the lakebed to see how far the same sediment layers had been displaced from each other vertically on either side of each fault. They found as the climate dried, the sides of the faults began slipping past each other more quickly, increasing at an average rate of 0.17 millimetres per year.

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“The main process is literally sort of clamping or unclamping this deformation zone, the zone of slip which results in earthquakes,” Scholz says. “A drier system and lower lake load allows it to slip more readily.”

Computer modelling suggested the reduced water mass also let more magma flow up from below the lake. One of the three volcanic islands in Lake Turkana erupted in 1888.

��è����Ƶs previously found lower sea levels increased volcanism at ocean ridges. But this is the first clear evidence of that happening around a lake, says at the University of California, Santa Barbara. “It’s almost like loosening the cork on a champagne bottle,” he says. “As you decrease that pressure, the magma is more likely to rise up in the crust and erupt.”

While increased rainfall due to climate change is now raising water levels in Lake Turkana once again, it would take thousands of years for that to significantly suppress earthquakes and volcanoes.

But assessments of seismic hazards should start considering how the changing climate might affect water levels, according to the study authors. And governments should take earthquake risk into account before they build or remove dams.

“They should put [seismometers] in before they make any huge changes,” Macdonald says.

A volcano seems to have been identified near the rim of Jezero crater on Mars, which is being explored by NASA’s Perseverance rover. The vehicle may have already sampled material spewed out by ancient eruptions.

Perseverance landed in Jezero crater in 2021 and has gradually made its way to the western rim, driving up a dried-up river, which is thought to have flowed about 3 to 4 billion years ago.

The rover has been collecting samples that were intended to be returned to Earth as part of the Mars Sample Return mission in the 2030s, although that is now threatened by the Trump administration’s proposed sweeping cuts at NASA.

Some of the material in the samples was thought to have been volcanic, including signs of lava flows. Now, at the Georgia Institute of Technology in Atlanta and his colleagues have found a possible source – a dormant volcano on the south-eastern rim of Jezero named Jezero Mons.

High-resolution imagery from Mars orbiters have revealed fine-grained material on the mountain, consistent with ash from a volcano. The size and shape of Jezero Mons – 21 kilometres wide and two kilometres tall – also matches similar volcanoes on Earth.

“An igneous volcano interpretation seems most consistent with the observations,” says Wray, one fuelled by magma from below the surface. “It’s the strongest case we can make without actually walking across it.”

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By counting craters near the volcano, Wray and his team estimate that Jezero Mons may have last erupted as recently as 1 billion years ago, possibly flinging ash, lava and rocks into Jezero crater, even as far as Perseverance’s landing site.

That means the rover might have collected samples from the volcano. If so, and if they could be returned to Earth, scientists would be able to precisely date the activity of a volcano on another planet for the first time.

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“You’d actually know when that volcano was active, which would be very cool,” says at Purdue University in Indiana, who is part of the rover’s science team. This could give us crucial information on “how the interior of the planet was evolving over time”, she says.

Even better, says Wray, would be driving Perseverance to the volcano itself, although that is unlikely to happen. “They’re driving in the opposite direction, because there’s really interesting ancient rocks outside the crater to the west,” he says. “I don’t blame them.”