Dec. 4, 2016

The Great Dying

The Permian mass extinction is called the Great Dying because 96% of species died out at that time. All life on Earth today is descended from the 4% of species that survived. The event was complex with at least two separate phases of extinction spread out over millions of years. Many causes have been proposed for the event, basalt flood eruptions, catastrophic methane release, drop in oxygen levels, sea level fluctuations or a combination of these. The end-Permian extinction event occurred 250 million years ago. It is often called the Great Dying because around 90 percent of marine species disappeared in a brief period, geologically speaking. Similar numbers died on land as well, producing a stark contrast between Permian rock layers beneath (or before) the extinction and the Triassic layers above. Extinctions are common throughout time, but this extinction event was much more devastating than the extinction event 65 million years ago, that wiped out the dinosaurs. Whatever happened during the Permian-Triassic period was much worse: No class of life was spared from the devastation. Trees, plants, lizards, proto-mammals, insects, fish, mollusks, and microbes -- all were nearly wiped out. Roughly 9 in 10 marine species and 7 in 10 land species vanished. Life on our planet almost came to an end.

Our planet was in the throes of severe volcanism at the end of the Permian. In a region that is now called Siberia, 1.5 million cubic kilometers of lava flowed from an awesome fissure in the crust. (For comparison, Mt. St. Helens unleashed about one cubic kilometer of lava in 1980.) Such an eruption would have scorched vast expanses of land, clouded the atmosphere with dust, and released climate-altering greenhouse gases.

World geography was also changing then. Plate tectonics pushed the continents together to form the super-continent Pangea and the super-ocean Panthalassa. Weather patterns and ocean currents shifted, many coastlines and their shallow marine ecosystems vanished, sea levels dropped. Plentiful charcoal-rich and soot-bearing beds found in sedimentary rock of the period are evidence of widespread wildfires, which played an important role in the rapid deforestation at the end of Permian. Scientists have found evidence of the release of an enormous quantity of methane gas as ice sheets melted at the end of a global ice age about 600 million years ago, possibly altering the ocean's chemistry, influencing oxygen levels in the ocean and atmosphere, and enhancing climate warming because methane is a powerful greenhouse gas.

Rocks also provide hard evidence, via carbon isotope signatures, of oceans under stress as the carbon cycle was reorganized and oxygen levels fell during the Great Dying.  Marine-organism fossils during the extinction period show a shift from normal species to those who could better tolerate low-oxygen waters. The animals died from a lack of dissolved oxygen in the water, and excess of carbon dioxide, a reduced ability to make shells from calcium carbonate, altered ocean acidity, and higher water temperatures. Sound familiar? All these changes happened rapidly, and each one amplified the effects of the others. Among the hardest hit were corals, along with sponges, shelled creatures and trilobites a dominant species during the Permian. Gastropods such as snails and bivalves such as scallops and clams became the dominant species after the Permian.

The Siberian Traps are the remnants of huge volcanic eruptions- flood basalt eruptions- that lasted for millions of years and contributed to the devastating Permian mass extinction. The eruptions sent catastrophic amounts of carbon gas into the atmosphere and the oceans. This led to long-term ocean acidification, ocean warming and vast areas of oxygen poor ocean water. The findings from paleologists about ocean conditions during the Great Dying match today’s trends in ocean chemistry. Currently carbon is being injected far faster than during the basalt floods of the Permian which began the extinction event during the Great Dying. Today, humans are far better than volcanoes in putting carbon into the atmosphere. Humans put over 25 billion tons of carbon into the atmosphere every year, while volcanoes put about 240 million tons per year. High concentrations of carbon-based gases in the atmosphere are leading to rapid acidification and warming of the oceans, as well as low-oxygen dead zones in the oceans. See the post on slime and jellyfish to understand how patterns of the past seem to be repeating in present ocean conditions.

The geologic record shows that once environmental deterioration is beyond the threshold or tolerance of the ecosystems, the ecosystems will collapse in a rapid way. But recovery will take a very long time.

The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so. The noxious atmosphere and acidic ocean conditions returned to a normal range, but the level of biodiversity didn't truly recover until 10 million years later. Life did recover, after many millions of years, and new groups emerged- the event had re-set evolution.

Our ocean conditions are similar today to the conditions of the Great Dying, yet we cannot seem to come together as a species to make the changes required to avoid such a devastating extinction event from happening again. Is it ignorance, disbelief, apathy or lack of political will that may be driving our own species to extinction?