The clathrate gun hypothesis suggests that methane clathrates on the ocean floor may have caused global warming and mass extinction in the past. Methane clathrates are methane gas trapped in water ice, found in low concentrations on continental shelves. The hypothesis depends on an external trigger, such as a volcanic eruption, melting the clathrates and releasing methane, which would warm the Earth and cause more clathrates to melt. This feedback effect would be devastating to all life on the planet. The hypothesis is the leading explanation for the Permian-Triassic mass extinction.
The clathrate gun hypothesis suggests that the mass release of methane from methane clathrates on the ocean floor may have triggered catastrophic global warming, in turn causing mass extinction, at least once in the ancient past of Earth. Methane clathrates refer to methane gas trapped within water ice, discovered deep beneath ocean sediments around the world. Methane clathrate is also sometimes referred to as methane hydrate or methane ice. Most of it is thought to have been formed by microbes that reduce (deoxidize) carbon dioxide, converting it into methane.
Methane clathrates are not found all over the ocean floor, only on continental shelves, the main area of the ocean hospitable to life, and even there, only found in low concentrations, about 1% by volume. However, compressed in an ice cage, methane has a relatively high density. One liter of methane clathrate can contain approximately 168 liters of methane gas. In addition, methane gas is about 62 times more potent a greenhouse gas than carbon dioxide. The clathrate gun hypothesis depends on the extreme of this heating effect.
The clathrate gun hypothesis begins with some external trigger, such as the creation of a large igneous province or the initial warming caused by sulfides released in a supervolcano eruption. The former is believed to have initiated the Permian-Triassic extinction, the largest mass extinction in history, killing 99% of all species on Earth. As approximately one million cubic kilometers of lava was released over the course of one million years, from a huge volcanic complex near the North Pole, huge amounts of lava seeped out of the volcano and onto the continental shelves, melting the methane clathrates and releasing methane.
Although methane only remains in Earth’s atmosphere for about 12 years, its release would have initiated a feedback effect, warming the Earth and making it more likely that more methane clathrates will melt. Under normal conditions, ice melts at 0°C (32°F), but methane clathrates, some buried under more than a kilometer of oceanic sediment, are under enough pressure to remain solid at temperatures as low as 18°C. C (64°F). But if the temperature rises above 18°C, methane clathrates are released, possibly in gigaton quantities. This would be devastating to all life on the planet.
The “gun” part of the clathrate gun hypothesis refers both to the fact that once it starts, it can’t be stopped, and to its lethal effects. Once the planet starts warming, circulation in the oceans will decrease, rendering large areas of the ocean anoxic, killing life in large numbers. Substantial data from the Permian-Triassic boundary has been found to sync well with the clathrate gun hypothesis, and it is now the leading explanation for the cause of the Permian-Triassic mass extinction.
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