Massihõljuste

Massihõljuste, also known as mass extinctions, are significant and widespread events in Earth's history where a large proportion of the planet's species disappear over a geologically short period. These events are characterized by a drastic decline in biodiversity, affecting numerous taxonomic groups across various ecosystems. While gradual extinctions occur constantly, mass extinctions are distinguished by their catastrophic scale and speed.

Scientists have identified several major mass extinction events throughout the Phanerozoic Eon, the most prominent being the Permian-Triassic extinction, often called the "Great Dying," which eliminated an estimated 96% of marine species and 70% of terrestrial vertebrate species. Other significant events include the Ordovician-Silurian, Late Devonian, Triassic-Jurassic, and Cretaceous-Paleogene (K-Pg) extinctions, the latter being famous for its role in the demise of non-avian dinosaurs, likely caused by an asteroid impact.

The causes of mass extinctions are diverse and often debated, but commonly cited factors include massive volcanic activity, asteroid or comet impacts, rapid climate change, sea-level fluctuations, and changes in ocean chemistry. These events can trigger cascading effects throughout ecosystems, leading to widespread ecological collapse. The study of massihõljuste provides crucial insights into the resilience of life on Earth, the factors that drive evolutionary change, and the potential vulnerabilities of current ecosystems. Understanding past extinction events is also considered vital for assessing the risks of ongoing biodiversity loss in the present day.