How giant volcanic eruptions alter Earth's climate

Earth’s climate has never stayed the same. Over millions of years, it has changed due to forces both deep inside the planet and far beyond it. Heat from within the Earth, shifting orbits around the Sun, and volcanic eruptions all shape the world we live in.

Scientists looked into past records to understand how Earth’s climate has changed. They studied old rocks and fossils to find clues linking climate shifts to big volcanic eruptions. These natural records reveal how Earth’s environment has evolved over time.

Forces that shape Earth’s climate

The inside of the Earth produces heat because some elements, like uranium, break down naturally over time. This process is called radioactive decay.

Along with this, volcanoes release heat and gases such as sulfur dioxide (SO₂) and carbon dioxide (CO₂) into the air. These gases can affect the climate by changing the temperature and composition of the atmosphere.

Earth doesn’t follow the exact same path around the Sun forever. Its orbit shifts slightly over time, changing how much sunlight reaches different parts of the planet. This affects the seasons, sometimes making them longer, shorter, warmer, or cooler.

These two processes – heat from inside the Earth and changes in sunlight – work together in complicated ways. Over thousands to millions of years, they affect the climate, shaping long-term patterns of temperature, weather, and ocean conditions.

Earth’s geological climate records

Study lead author Thomas Westerhold is a researcher at MARUM – Center for Marine Environmental Sciences at the University of Bremen.

“Just like a metronome, we used the rhythmic changes in solar insolation imprinted in geological data to synchronize geological climate archives from the South Atlantic and the Northwest Pacific,” said Westerhold.

”These key records span the last million years of the Cretaceous and are synchronized down to 5,000 years or less, geologically a blink of an eye 66 million years ago.”

Accurately aligning geological records allows scientists to identify simultaneous climate events across regions.

“So, we had the geological records perfectly lined up in time, and observed that two major changes in climate and biota occurred at the same time in both oceans. But we had to find a way to test if these changes are caused by large-scale volcanic eruptions related to the Deccan Traps in India,” said Westerhold.

Deccan traps and their impact

In western India, there is a massive area of solidified lava called the Deccan Traps. The lava layers are extremely thick, reaching up to two kilometers in some places.

Scientists call this kind of large-scale volcanic activity a Large Igneous Province, which means a region covered by huge amounts of volcanic rock formed from repeated eruptions.

Huge volcanic eruptions in Earth’s past have greatly affected life. When volcanoes erupt this much, they release large amounts of gases like CO₂ and SO₂.

These gases can change the air and oceans, impacting Earth’s climate, air quality, and sea life. Sometimes, these changes were so severe that they caused mass extinctions, wiping out many species.

Volcanic influence in ocean records

“The formation of the flood basalts and its subsequent weathering will leave a geochemical fingerprint in the ocean,“ said study co-author Junichiro Kuroda (University Tokyo, Japan), who conducted the geochemical analyses.

“Therefore, we measured the Osmium isotope composition of the South Atlantic and the Northwest Pacific deposits. They should show the same fingerprint at the same time.”

The study revealed two distinct shifts in the Osmium isotope composition in both oceans. These shifts aligned with major eruption phases of the Deccan Traps in the late Cretaceous period.

“To our surprise we found two steps in the Osmium isotope composition in both oceans contemporaneous with major eruption phases of the Deccan Traps in the latest Cretaceous. And even more surprising those steps had different impacts on the environment as recorded by fossil remains in the drill cores,” said Westerhold.

Measuring massive volcano events

Scientists used advanced models to make sense of the data. They created simulations to see how volcanic gases affected Earth’s climate. These models helped them estimate how big the eruptions were and how they changed the atmosphere.

“The volume of the erupted flood basalt must have been much larger than previously thought during this early phase of Deccan Trap volcanism. And the related distinct emissions of carbon and sulfur dioxide had diverse effects on the global climate system,” explained Don Penman (Utah State University, USA) who did the geochemical modeling.

According to these findings, a significant eruption phase occurred 66.288 million years ago, independently dated using radioisotopic methods. This phase likely included an initial pulse of sulfur-rich eruptions, causing ecological stress both locally and globally.

These discoveries refine our understanding of how massive volcanic events influence Earth’s climate and ecosystems over geological timescales.

The study is published in the journal Science Advances.

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