Around 700 million years ago, Earth experienced one of its most extreme climate events — a period known as “Snowball Earth,” during which the entire planet is believed to have been encased in ice, even at the equator. For years, scientists have debated what pushed the planet into such a deep freeze. Now, new research offers a compelling explanation: a combination of massive volcanic activity and the absence of plant life.

The study, published in the Journal of Geophysical Research: Planets, points to the Franklin Large Igneous Province — a massive series of volcanic eruptions that occurred roughly 720 million years ago. These eruptions blanketed what is now Alaska, northern Canada, and Greenland in fresh volcanic rock. Unlike other periods of intense volcanism in Earth’s history, the Franklin eruptions happened during an already cool climatic phase — and that, researchers argue, made all the difference.

In the absence of land plants, which had not yet evolved, the exposed volcanic rock underwent rapid weathering. This process involves chemical reactions between rock, rainwater, and carbon dioxide (CO₂) in the atmosphere. As the weathering accelerated, it pulled vast amounts of CO₂ — a key greenhouse gas — out of the atmosphere.

The researchers used climate models to show that the sheer scale of this erosion was enough to significantly lower global temperatures. With greenhouse gases depleted and little heat trapped in the atmosphere, Earth’s climate spiraled into a self-reinforcing glaciation, covering nearly all land and sea surfaces in ice.

Interestingly, similar large-scale eruptions in other eras didn’t lead to global glaciation. The study explains that in those cases, the Earth was generally warmer, or land surfaces were covered by plants that slowed down weathering and the removal of carbon dioxide.

This research offers new insight into how Earth’s geological and biological evolution has shaped its climate in profound ways — and how seemingly small shifts in natural systems can trigger dramatic global transformations.