April 1, 2014

A single-celled organism that was a glutton for nickel may have played a key role in the most devastating mass extinction in Earth’s history. The Permian Extinction took place some 252 million years ago. It is informally known as “The Great Dying” because at least 90 percent of all living species on Earth perished over the short (geologically speaking) period of about 60,000 years. Even insects, which largely escaped other mass extinctions, were hit hard. Scientific theories for the die-off have included global warming, global cooling, meteorite impacts, disease, blasts of radioactive cosmic rays from space, and–the favorite–massive volcanic eruptions. Volcanoes have come under suspicion because of the Siberian Traps, about 480,000 cubic miles (2 million cubic kilometers) of preserved flood basalts (layers of volcanic rock) dating from the end of the Permian Period in western Siberia. In the longest-known continuous volcanic eruption in Earth’s history, Siberian volcanoes spewed out enough lava to cover Earth to a depth of 10 feet (3 meters).

Now a team of researchers headed by Daniel Rothman of the Massachusetts Institute of Technology is arguing that the volcanoes were only “accessories to the crime.” The main cuplrit, they contend, was a group of microbes called Methanosarcina. These methane-producing microbes are archaea, organisms that make up one of three basic divisions of life. According to the researchers, Methanosarcina grew explosively in the oceans, releasing massive amounts of methane. Methane is an even more potent greenhouse gas than carbon dioxide (CO2). In fact, molecule for molecule, methane traps about 25 times as much atmospheric heat as does CO2. The methane from the microbes dramatically changed the chemistry of the atmosphere and the oceans, making Earth’s climate toxic to nearly all species.

Mount Etna is an active volcano on the island of Sicily. Major eruptions of the volcano spew molten lava and endanger nearby villages. The eruption shown here began on July 18, 2001. AP/Wide World

Rothman and his team presented three lines of evidence to support their theory. First, they pointed to a huge increase in CO2 levels in the oceans at the end of the Permian Period. As ocean waters absorbed the CO2, they would have become increasingly acidic. Devastating losses in marine organisms, particularly those with shells, would have resulted. Second, the researchers determined that about 251 million years ago, Methanosarcina picked up a gene from another microbe that enabled it to rapidly convert carbon into methane. Even with practically unlimited amounts of carbon at their disposal, the microbes would still have needed an esssential nutrient–nickel–to support their new lifestyle. According to the scientists, that’s where the Siberian volcanoes came in. Lava from the volcanoes produced the world’s largest nickel deposits. The nickel somehow reached the oceans, causing a feeding frenzy among the microbes. That explosion in atmospheric methane essentially suffocated most of the life on Earth.

After the Permian extinction, life took at least 5 million years to recover–that is, to evolve a wide variety of species. In the oceans, complex mollusks, crustaceans, and fish, which could swim easily from place to place, become more widespread and common. On land, surving plants and animals evolved into a variety of forms, including coniferous trees and insect-eating mammals. The extinctions of Permian animals also paved the way for the dinosaurs.

Additional World Book articles:

• Methane: Another Greenhouse Troublemaker (a Special Report)
• The Biggest Eruptions on Earth (a Special Report)
• The Ocean’s Changing Chemistry: Tipping the Balance? (a Special Report)