Scientists have identified the cause of Earth's greatest mass extinction, explaining why clams and snails dominate modern beaches [1].

This discovery provides a critical link between ancient climatic shifts and the current composition of marine ecosystems. By understanding which species survived this prehistoric crisis, researchers can better predict how current ocean warming might reshape biodiversity.

According to a study published this week, the extinction event was driven by a combination of warming oceans and falling oxygen levels [1]. These environmental stressors wiped out animals that were unable to adapt to the changing chemistry of the water [1]. This process cleared the way for species with body plans better suited for low-oxygen environments to thrive and eventually dominate the seas [1].

Researchers said the answer to why certain mollusks are so prevalent today lies in this specific period of instability. The study suggests that the survivors of this event were those capable of enduring the harsh conditions that killed off their competitors [1].

"Scientists finally solved the mystery of Earth’s greatest mass extinction," researchers said in a report published by ScienceDaily [1]. The findings highlight the selective nature of mass extinctions, where survival is often a matter of physiological luck rather than sheer strength.

"A new study suggests the answer lies in Earth's greatest mass extinction, when warming oceans and falling oxygen levels wiped out animals that couldn’t adapt," researchers said [1]. The research underscores how a single global event can permanently alter the trajectory of evolution on a planetary scale.

“Warming oceans and falling oxygen levels wiped out animals that couldn’t adapt.”

This finding demonstrates that the current biological makeup of the world's oceans is not random, but the result of a selective filter created by climate stress. By identifying the specific environmental triggers—temperature and oxygen—that favored clams and snails over other organisms, scientists can create more accurate models for how modern anthropogenic climate change may trigger similar selective extinctions in current marine life.