When the ocean retreats, does it trigger the planet's most devastating mass extinctions?

Nature · Published 3 October 2026 Swipe more like this →

In short: Marine regression occurs when sea levels drop, exposing vast stretches of previously submerged seafloor. While these geological shifts are often linked to the world's most catastrophic extinction events, scientists debate whether they are the primary drivers of biological collapse or merely symptoms of deeper, more volatile planetary processes at work.

A marine regression is the geological inverse of a transgression, where rising waters flood the land. These retreats are often tied to fluctuations in plate tectonic activity. One prominent hypothesis suggests that a slowdown in sea-floor spreading causes mid-ocean ridges to occupy less volume, effectively lowering the global sea level. Such tectonic shifts are frequently associated with massive volcanic episodes, including the formation of the Siberian and Deccan Traps, which are themselves major drivers of environmental instability.

The fossil record reveals that regressions correlate with significant mass extinctions, such as the Permian–Triassic event 250 million years ago and the Cretaceous–Paleogene event 66 million years ago. During the Permian–Triassic extinction, the largest in Earth's history, sea levels plummeted by 250 meters. While the loss of shallow-sea habitats explains the demise of marine life, it is less clear how these changes would devastate terrestrial species. Consequently, many researchers view regressions as symptoms of broader environmental crises rather than the sole cause of extinction.

Glaciation provides a more direct mechanism for sea-level change. During the Pleistocene, the growth of ice sheets locked up vast quantities of water, causing sea levels to drop. At the peak of the last ice age 18,000 years ago, levels were 120 to 130 meters lower than today. A similar cold spell 6 million years ago triggered a regression that initiated the Messinian salinity crisis in the Mediterranean. However, not all regressions fit this pattern; the regression accompanying the end-of-Cretaceous extinction remains a notable outlier, suggesting that the causes of these dramatic retreats are as varied as the geological history of the Earth itself.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Earth's history is defined by five catastrophic, and sometimes mysterious, mass extinctions
• Why the greatest mass extinction left us with seashells instead of brachiopods
• The Great Dying wiped out about 81 percent of marine species
• The Great Dying wiped out 81 percent of marine species in a geological blink
• Did a global deep freeze turn Earth into a giant, ice-covered snowball?
• Is the Earth's solid interior actually flowing like a slow-moving, heated liquid?
• Ancient Grand Canyon mudstones reveal how Earth’s orbit looked 1.2 billion years ago
• Why this vibrant green mineral was once feared as a copper-stealing demon
• Before humanity mastered smelting, our only source of iron fell from the stars
• Why you cannot identify an earthquake's true scale until the shaking finally stops
• This common mineral is a master of ice formation and massive crystal growth
• Earth’s magnetic field is shifting, creating a massive, radiation-prone weak spot over the Atlantic.

More in Geology · More in Nature · Latest · A–Z · All topics