Permian–Triassic extinction event

Permian–Triassic extinction event
Name	Permian–Triassic extinction event
Date	c. 251.9 million years ago
Location	Global
Type	Mass extinction
Cause	Siberian Traps volcanism, marine anoxia, global warming
Affected	Marine and terrestrial life
Extinction rate	~81% of marine species, ~70% of terrestrial vertebrate species
Preceded by	Capitanian extinction event
Followed by	Triassic–Jurassic extinction event

Permian–Triassic extinction event. Occurring approximately 252 million years ago, it marks the boundary between the Permian and Triassic periods. This catastrophic event, often called the "Great Dying," represents the most severe loss of life in Earth's history, profoundly reshaping the planet's biosphere and paving the way for the rise of the Mesozoic Era.

Introduction

The event unfolded during a geologically brief interval at the end of the Paleozoic Era. It coincided with the final stages of the assembly of the supercontinent Pangaea, which created vast interior deserts and altered global climate patterns. The extinction profoundly impacted all ecosystems, from deep ocean basins to continental interiors, and its effects are recorded in rock formations worldwide, such as the Meishan section. This global catastrophe reset the evolutionary trajectory of life, leading to the dominance of new groups like archosaurs and eventually dinosaurs.

Extinction Statistics

An estimated 81% of all marine species perished, including entire groups like the trilobites, blastoids, and most rugose corals. On land, approximately 70% of terrestrial vertebrate species disappeared, devastating the dominant therapsids and pelycosaurs. Iconic Paleozoic forests, dominated by glossopteris flora, collapsed. The loss of biodiversity was so extreme that it took ecosystems millions of years to re-establish complex community structures, with surviving groups like bivalves and ammonoids undergoing dramatic radiations in the aftermath.

Causes

The primary driver is strongly linked to massive volcanism from the Siberian Traps, a large igneous province in modern-day Russia. This volcanism released enormous quantities of carbon dioxide, methane, and sulfur dioxide, triggering extreme global warming and ocean acidification. Subsequent cascading effects included widespread marine anoxia, where oxygen-depleted waters spread across ocean basins, as evidenced by deposits of black shale. Potential contributing factors may have included methane release from clathrate deposits and a resultant sharp increase in global temperatures, creating a lethal "hothouse" climate.

Effects on Life

In the oceans, reef ecosystems, built by organisms like tabulate corals, were completely obliterated. The loss of primary producers disrupted entire food webs, leading to the collapse of marine communities from the photic zone to the seafloor. On land, the dominant vertebrate faunas, including formidable predators like the gorgonopsia, were decimated. The widespread aridity across Pangaea and catastrophic climate shifts led to the replacement of seed fern forests by more resilient flora, such as lycophytes, in the early Triassic.

Recovery

Biological recovery was remarkably slow, spanning 5 to 10 million years into the Middle Triassic. Early Triassic ecosystems were depauperate, dominated by disaster taxa like the hardy bivalve Claraia. The delay in recovery is attributed to persistently harsh environmental conditions, including repeated anoxic events and high temperatures. The eventual re-establishment of complex marine communities, including new scleractinia corals, and the terrestrial radiation of archosaurs and cynodonts, set the stage for the Mesozoic world.

Geological Evidence

The global stratigraphic signature is marked by a thin clay layer found in sections from Meishan to the Dolomites. This layer shows a sharp negative excursion in the ratio of carbon isotopes, indicating a massive disruption to the carbon cycle. Widespread deposits of chert and black shale point to silica-rich, anoxic ocean conditions. The timing is precisely constrained by uranium-lead dating of zircon crystals from volcanic ash beds interlayered with extinction horizons, which correlate perfectly with the onset of the Siberian Traps eruptions.

Category:Extinction events Category:Permian Category:Triassic