Great Dying

Great Dying
CC BY-SA 3.0 · source
Name	Great Dying
Caption	The Permian–Triassic boundary at Guryul Ravine, Kashmir, a key site for studying the event.
Date	c. 251.9 million years ago
Location	Global
Type	Mass extinction
Cause	Siberian Traps volcanism, anoxia, global warming
Affected	Marine life, terrestrial life
Extinction count	~81% of marine species, ~70% of terrestrial vertebrate species
Preceded by	Late Devonian extinction
Followed by	Triassic–Jurassic extinction event

Great Dying. The Great Dying, formally known as the Permian–Triassic extinction event, was the most severe mass extinction in Earth's history, occurring approximately 252 million years ago at the end of the Permian period. It devastated life in the oceans and on land, eliminating an estimated 81% of marine species and 70% of terrestrial vertebrate species. The event profoundly reshaped the course of evolutionary history, paving the way for the rise of Mesozoic faunas, including the ancestors of dinosaurs and mammals.

Overview

The event marks the boundary between the Permian and Triassic periods, a transition visible in the geological record worldwide. Key fossil sites documenting the catastrophe include the Meishan section in China and the Karoo Basin in South Africa. The extinction was not instantaneous but occurred in multiple pulses over a period of roughly 60,000 years, as indicated by studies of zircon crystals from volcanic ash layers. This crisis ended the dominance of ancient lineages like the Paleozoic's trilobites and Pelycosaurs, creating ecological vacancies that were eventually filled by new groups during the Mesozoic Era.

Causes

The primary driver is widely linked to massive volcanism from the Siberian Traps, a large igneous province in modern-day Russia. Eruptions released enormous quantities of carbon dioxide, methane, and sulfur dioxide, triggering extreme global warming and ocean acidification. This volcanism likely ignited vast coal deposits, further amplifying greenhouse gas emissions. Concurrently, warming oceans became stratified, leading to widespread anoxia and the release of toxic hydrogen sulfide from bacteria like green sulfur bacteria. These cascading effects created a lethal combination of rapid climate change, oxygen deprivation, and toxic conditions.

Extinction patterns

In the oceans, groups like the trilobites, blastoids, and rugose corals were eradicated entirely, while others such as the brachiopods and crinoids suffered catastrophic declines. Reef ecosystems, dominated by organisms like the tabulate corals and Archaeocyatha, collapsed completely and would not reappear for millions of years. On land, the extinction severely impacted the dominant therapsids, including the dinocephalians and gorgonopsians, as well as many insect orders. Surviving groups, like the Lystrosaurus and early archosaurs, were typically small, generalist organisms.

Geological evidence

The Permian–Triassic boundary is globally identified by a sharp negative excursion in carbon-13 isotopes, recorded in marine carbonate rocks and organic matter, indicating a massive disruption to the carbon cycle. Layers from this period often contain fungal spores, suggesting widespread decay of dead forests. Evidence of anoxia is found in the deposition of black shales and the presence of pyrite framboids. In regions like Greenland, lava flows from the Siberian Traps are contemporaneous with the extinction horizon, providing a direct chronological link.

Recovery and aftermath

Biological recovery was exceptionally slow, taking an estimated 4-6 million years into the Middle Triassic, due to persistently harsh conditions. Early Triassic ecosystems were depauperate, dominated by disaster taxa like the Lystrosaurus on land and Claraia bivalves in the seas. The vacant ecospace eventually allowed for the diversification of new groups, including the first true dinosaurs, pterosaurs, and crocodylomorphs. This period also saw the rise of the first mammaliaforms from surviving cynodont therapsids, setting the stage for future Mesozoic and Cenozoic faunas.

In popular culture

The event has been featured in documentary series such as the BBC's Walking with Monsters and the National Geographic special Earth: The Making of a Planet. It serves as a central plot element in novels like Robert J. Sawyer's Calculating God and is discussed in popular science books by authors like Peter Ward in Under a Green Sky. The severity of the Great Dying is often cited in discussions about modern climate change and the Holocene extinction.

Category:Mass extinctions Category:Permian Category:Triassic Category:Anoxic events