Deccan Traps
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Dinosaurs and the Deccan Traps

Earth Springs a Leak

We all learned in primary school how the dinosaurs went extinct when a giant asteroid slammed into Earth about 65 million years ago. But there is a backstory about an already weakened biosphere that doesn’t get much press. The story of the Deccan Traps, a massive outpouring of flood basalts on the Indian continent, introduced rapid climate change into the extinction equation.

The term “traps” describes flood basalt provinces. The term derives from the Swedish word “trappa” meaning stairs. It is a reference to the stair-like morphology of stacked basalt sheets when they erode.

We live on the solid crust of our planet. But below us in Earth’s mantle, a molten planet churns. Our solid crust floats on slowly moving currents of magma that pull and push tectonic plates around the planet’s surface.

Occasionally, massive plumes of fluid mantel push through Earth’s crust, making their way to the surface. When they erupt, more than just simple volcanos appear. The earth splits open along massive fissures, and molten magma disgorges onto the surface of the planet. Rivers of lava flow like water across Earth’s surface, filling in valleys with lakes of molting rock, and traversing the topography like a flood from hell. Individual flows travel hundreds of miles before they freeze into solid rock. These outpourings produce flood basalts.

Some of the most devastating mass extinction events in geological history are connected to episodes of flood basalts. The devastation is less about the basalt and more about the gases released into the atmosphere — volcanic vents and degassing magma pump carbon dioxide, methane, sulfur dioxide, mercury, and more into Earth’s air.

The Deccan Traps

Sputtering remnants from the mantle plume responsible for the Deccan Traps still pump lava through one of the most active volcanoes on the planet, Réunion, a French island in the western Indian Ocean. Despite its hyperactive eruption schedule, the island’s volcanoes are insignificant compared to the glory days of the Deccan Traps. An estimated 600,000 cubic miles of liquid rock extruded onto Earth’s surface 65 million years ago, enough to cover Texas, California, and Montana.

Recent work on the mantle plume responsible for the Deccan Traps shows it to be tree-like. Approximately 1,500 kilometers below Earth’s surface lies the central trunk. Sprouting from the trunk are three branches, each extending towards the surface and feeding various Indo-Austral hotspots.

Eruption of the Deccan flood basalts took less than a million years, a geological blink of an eye. Human beings have been vigorously polluting the atmosphere for about 200 years, but the Deccan Traps spewed toxins and greenhouse gases for 700,000 years. The Chicxulub asteroid impact near the Mexican, Yucatán peninsula was the coup de grâce for an already weakened biosphere.

The Deccan Traps are Not Alone

The flood basalts from the Deccan Traps are not a one-off event. The most disastrous extinction event in the geological records, the Great Dying, was also connected to flood basalts.

Ninety-five percent of Earth’s marine species and seventy percent of its terrestrial species vanished at the end of the Permian, 250 million years ago. This event was, without question, the most severe of all mass extinctions to threaten the biosphere during the history of our planet. Half of all existing taxonomic families disappeared.

Located in the northern regions of Siberia are the remnants of another massive outpouring of flood basalts called the Siberian Traps. These flood basalts erupted at the end of the Permian and covered an area estimated at seven million square kilometers. For two million years, liquid rock poured from the earth in flood after flood. When the devastation finally stopped, one million cubic miles of rock had been pushed onto Earth’s surface. The degassing of the new magma led to an assault on life.

Earth’s atmosphere retained increasing amounts of heat as carbon dioxide and methane accumulated in the atmosphere, leading to global warming and climate change. The blow dealt to life at this time was due more to the rate of change than to change itself. Earth’s climate is always slowly changing, and life responds to these changes through evolution. But when change is too rapid, life cannot evolve fast enough to outpace climate change, and huge portions of the biosphere pass into the void of extinction.

Today we need to reflect on the events surrounding the Deccan and Siberian Traps, and their effect on life. Flood basalts are not the only way to flood the atmosphere with greenhouse gases, creating runaway global warming and mass extinctions. The constant burning of fossil fuels can do the same.

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William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.