Late Ordovician Mass Extinction

Late Ordovician mass extinction (LOME) is also known as the Silurian extinction of the Ordovician. They are the second largest of major five extinction events that happened on the planet. The first major was the mass extinction in the Permian Triassic.


LOME has caused the elimination of about 85% of marine species from the planet Earth. Killed more than one-third of brachiopods and bryozoa. It also destroyed some conodonts, corals, trilobites, echinoderms, graptolites and clams. LOME did not affect the ecosystem of other mass extinction-like structures.

Following LOME, the biodiversity that was lost was restored in the first 5 million years duringthe Silurian period.  LOME occurred in two different pulses named Hirnantian and Katian. During the first pulse of Lome, called Katian, the Earth changed from a greenhouse climate to an icy cold climate. It led to the freezing of the continent. The glacial zone of the continent was centered on the Gondwana continent, which was in Antarctica at that time. The sinking sea level and cooling destroyed the habitat. The drop in temperature killed some creatures.

During LOME’s second impulse, called the Hirnantian, the glacier receded and returned to warmth. Hirnantians are associated with anoxia which means oxygen deficiency and normal anoxia which means sulphide production. Ordovician bio diversification event followed LOME. This is the largest evolutionary wave in the planet’s biological history.

The main causes of LOME were thought to be periglacial zones, anoxia and normal oxygenises. However, the cause is controversial.

Findings about LOME in the year 2021

The most controversial topic of the late Ordovician mass extinction is whether ocean oxygen caused the extinction. In the month of November, 2021, a group of scientists solved this problem. They found that oxygen was not a factor in Lome. In fact, at that time, there was no oxygen in the deep sea. Lome was caused by the cooling of the climate. This finding that oxygen was not involved in species extinction is important because it invalidates some hypotheses about the relationship between temperature changes, species extinction and oxygen levels.

5 Major mass extinction events

Devonian Extinction which occurred 365 million years ago, Ordovician-Silurian Extinction which occurred 440 million years ago, and Permian-Triassic extinction which occurred 250 million years ago, Cretaceous-tertiary Extinction which occurred 65 million years ago and Triassic-Jurassic Extinction which occurred 210 million years ago.


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