Causes of Mass Extinction

The Ends of the World

By Peter Brannen A great book about the Earth’s past mass extinctions, ancient worlds, their remains, and the people who study them.

There are Five Big Mass Extinctions

Historic mass extinctions seem to be closely related to massive swings in CO2 rocking the global climate. Three out of five mass extinctions seem to be caused by the CO2 release from mass contiental size volcanic flows. One seems to have been caused by CO2 drops from plant life. The last one was maybe rock weathering kept in check by volcanoes until they stop and termination shock froze the planet.

First here is a basic principle determining ancient climate: CO2 is absorbed over millions of years by rock weathering. It is also re-released by volcanoes. These volcanoes expose rock which restarts the cycle.¹

The Ordovician mass extinction

• Rock weathering on a mountain chain freezing earth. Perhaps a termination shock of a volcanic chain stopping.
• 100,000 years long (2 pulses)
• 85% of life died
• Kill method:
• Pulse 1: Volatile climate changes. It was a warm period with 8x more CO2 than today. Mountian chains were uplifted 20mya before extinction. There were 500,000 sq mile ash beds from volcanoes, but they were 10mya before the exinction. (No impact at the time, actually a time of biodiversity increase.) Maybe the volcanoes were countering the temperature drop until they shut off and the termination shock caused a sudden freeze by 5C all at once. A lot of the life were in shallow seas the size of continents. These dried up when ice formed. There was no place to migrate away from the ice because Gondwana was at the south pole, which also increased the ice mass. An increase in oxygen happened which worsened the extinction. There were die offs from ocean oxygenation
• Pulse 2: Sudden warming caused a melt, the melt caused circulation, the circulation caused O2 at the ocean floor, which caused die offs at the bottom of the food chain, and the food chain collapsed.

Images from Hildreth Meière’s incredible mosaic.

The Devonian mass extinction

• Plants spreading over land. (Mass depletion more than mass extinction.)
• 20,000,0000-25,000,0000 years long
• 75% of species
• Kill method: A 90% drop in CO2. 35% of the atmosphere was O2. There were pulses of climate change, perhaps to due to pulses of evolution of life on land. (seeds invented, push inland, trees invented, colonize new niches, roots invented, push inland) There were also volcanic erruptions in Russia/Ukraine. Warming may have caused rising sea levels, with anoxia wiping out everything on the ocean shelves. Another freeze occurs all the way to the equator. Presumably from weathering the newly exposed rock. The Pangaea continent made it so there was less room for diversity and escape to better climates, and less room for speciation. Mostly this extinction is a mystery.

The Permian mass extinction

• Siberian traps - continental size volcanic flows
• 2 million square miles, 2.5 miles deep in some places
• 60,000 years long
• 95% of species
• Kill method: Insane levels of CO2. The Siberian Trap flows not only released CO2, they ignited coal basins, which (exploded and) released even more CO2 and methane. There were about 10,000-48,000 gigatons of CO2 per year. A 16C rise in temperatures causing hot-tub temperature ocean. Ocean pH falls and pteropods can’t form shells so they entirely die (bottom of the food chain). The CO2 caused warm water, which lessens O2 dissolved in water. The life needs more O2 in warm temperatures causing a vicious cycle. Eventually anarobic bacteria thrives and release poisonous hydrogen sulfide. These may have been spread everywhere by crazy hurricanes due to high temperatures (100 degree water). Green slime world results. Complicating issues from the lava flows were 1) sulfur aerosols which blocked the sunlight causing winters, 2) noxious volcanic gases across the land, 3) toxic levels of methane and CO2, 4) salt deposits erasing the ozone, 5) phosphorous releases causing plankton blooms and hypoxia.

The high temperatures lingered, anoxia lasted for 5 million years, slowing the world’s recovery.

The Triassic mass extinction

• Central Atlantic Magmatic Province - continental size volcanic flows
• 4 million square miles
• 20,000 years for first pulse of 75% and over 600,000 all 4 pulses of extinction
• 80% of species
• Kill method: High CO2, +3 degrees Celsius. Raising sea levels means reefs have to grow upslope, but can’t grow in the acidified oceans. Ocean floor methane releases worsened the cycle. Including possible swings from sulfates (3 year long freezing spells)

The Cretaceous mass extinction

• Deccan Traps²
• Over 200,000 square miles, 2 miles deep in some places
• 100-10,000 years
• 75% of species
• Kill method: Greenhouse earth previously for thousands of years, the first 4% of Deccan Traps lava created a warm spike, ocean acidification, followed by an icy plummet of 8C from rock weathering for a short bitter cold glacial spell. The Chicxulub asteroid may have triggered the volcanic release of 70% of the Deccan lava flow. Tsunamis from the impact cause collapse of the eastern seaboard shores into the ocean which kills the life there. Dust from the impact darkens the sunlight for years causing plankton die off and food web collapses. The CO2 release acidifies the ocean also causing die offs. It remains super hot for thousands of years.

Side note - Not a mass extinction because there was biodiversity forming simultaneously, but there was a mass extinction caused by evolution: Edicarian - Cambrian explosion was also a mass extinction of previous life forms. Biological behavior change drove the extinction/diversification - burrowing destroyed previous food. Sight caused hunting. Oxygen level changes, and clean water were radical shifts. Anoxic water caused the “Cambrian Dead Interval”