The planet's greatest killer
Around 252 million years ago, the ground in modern-day Siberia split open. This was not a single volcanic cone erupting, but enormous fissures in the Earth's crust that poured out curtains of fluid basaltic lava for roughly two million years. This event, known as the Siberian Traps, was one of the largest known volcanic events in the last 500 million years. The total volume of erupted material is estimated at around 4 million cubic kilometers, enough to cover an area of about 7 million square kilometers. The source is believed to have been a mantle plume that rose from deep within the Earth and struck the base of the Siberian Craton.
The eruptions straddled the boundary between the Permian and Triassic geological periods, coinciding precisely with Earth's most severe extinction event: the "Great Dying." This was no coincidence. The volcanism triggered a cascade of environmental changes that eliminated up to 96% of all marine species and 70% of terrestrial vertebrate species. The event was so deep it changed the evolutionary path of life on Earth. The once-dominant trilobites vanished completely, along with vast swathes of other marine and land-based life.
A world choked and poisoned
The lethality of the Siberian Traps came from the lava, but from the colossal volume of gas released into the atmosphere. The magma didn't just pour out; it also intruded into thick layers of sedimentary rock beneath the surface, including vast coal basins and carbonate deposits. This process effectively "cooked" the surrounding rock, releasing immense quantities of greenhouse gases and toxic compounds.
Atmospheric carbon dioxide levels surged from around 400 parts per million to 2,500 ppm. Over the course of the eruptions, an estimated 100,000 billion metric tons of carbon dioxide were released, leading to extreme global warming. Global temperatures jumped by as much as 10 degrees Celsius. Ocean temperatures in the equatorial regions may have exceeded 40°C (104°F).
The eruptions also belched out thousands of gigatons of sulfur dioxide, chlorine, and fluorine. The sulfur dioxide created intense acid rain, which stripped the land of vegetation and altered soil chemistry. In the oceans, it dissolved to form sulfuric acid, causing a rapid drop in pH that was devastating for organisms with calcium carbonate shells. The combination of a warm and acidic ocean created a deadly environment, leading to the near-total collapse of marine ecosystems.