Over the 4.6 billion years of Earth's history, life has experienced five mass extinctions. These are known as the "Big Five."
Traditionally, the causes of these extinction events were thought to be "meteorite impacts" or "unexplained climate change," but entering the 2020s, advances in mass spectrometry technology and geochronology are fundamentally overturning that understanding.
Recent research reveals that many past extinctions originated from internal Earth activity, specifically massive volcanic activities known as "Large Igneous Provinces (LIPs)."
The 1st - End-Ordovician Mass Extinction
Occurring about 443 million years ago, this mass extinction wiped out 85% of all species. Latest research has revealed that this extinction occurred in two stages (two waves).
Ordovician trilobite
The First Wave: Global Cooling
Previously, the cause of this extinction was explained as "the onset of an ice age accompanying the movement of the Gondwana supercontinent," but why it suddenly cooled was a long-standing mystery. However, recent research is identifying the true culprit.
"Abnormal mercury concentrations" matching this period have been discovered in strata around the world. Mercury is the evidence (fingerprint) of massive volcanic activity. Research since 2022 has identified the massive eruption of the "Alborz Large Igneous Province (Alborz LIP)," which existed from present-day northern Iran to Australia.
During the weathering process of the basalt released by this massive eruption, it rapidly absorbed carbon dioxide (CO₂) from the atmosphere. This "rapid removal of CO₂" is thought to be the true cause that cooled the Earth and triggered the ice age.
The Second Wave: Global Warming and Anoxia
The extinction event didn't end with just cooling. About 500,000 to 1 million years later, at the end of the ice age, rapid warming occurred. As glaciers melted and sea levels rose, oxygen-poor bottom waters flowed onto the continental shelves, causing widespread "oceanic anoxic events."
The organisms that had adapted and survived the first wave of cooling could not withstand the completely opposite environmental changes of "scorching heat and oxygen deprivation" in the ensuing second wave, and many perished. Behind the disappearance of once-thriving brachiopods, conodonts, and trilobites was this relentless, "double-whammy" environmental fluctuation.
The 2nd - Late Devonian Mass Extinction
About 374 million years ago, decreasing oxygen levels in the oceans and global cooling progressed, causing 82% of species to go extinct. Many marine organisms such as armored fish and Dunkleosteus perished, and coral reef ecosystems were dealt a devastating blow.
The cause of this extinction event had also long been debated, but a connection to the massive volcanic activity of the "Viluy Traps" in Siberia has become clear.
Latest analyses have detected a volcanic "mercury spike" in the strata where the extinction occurred. The eruption of the Viluy Traps not only scattered toxic metals but also accelerated the weathering of land plants through climate change. As a result, massive amounts of nutrients flowed into the sea, causing an explosive proliferation of plankton. Oxygen was consumed to decompose their remains, leading to widespread "anoxic conditions (oceanic anoxic events)" in the oceans.
Relatively freshwater species that were resilient to oxygen concentration changes (such as fish living in rivers and swamps) survived, but marine species suffered catastrophic damage. Following this, the advancement of amphibians onto land accelerated, as if to move into the newly vacant ecological niches.
The Hidden Mass Extinction - End-Capitanian (About 260 million years ago)
Latest Research Topic: The Big Six?
Recent research has made it almost certain that there was another independent mass extinction event about 8 million years prior to the end-Permian mass extinction. This is called the "End-Capitanian mass extinction," and there is growing discussion that it should be called the "Big Six" in addition to the "Big Five."
In the middle of the Permian period, the Emeishan Large Igneous Province (Emeishan LIP) in southwestern China erupted. A feature of this eruption was that magma pierced through sedimentary layers such as limestone, generating massive amounts of "methane," a potent greenhouse gas.
As a result, about 60% of marine species went extinct, and corals, fusulinids, and the large-headed reptiles known as "Dinocephalians" disappeared from the Earth. This event served as a prelude to the worst extinction in history that was to follow.
The 3rd - End-Permian Mass Extinction
Occurring about 252 million years ago, it is believed that 95% of marine life and over 90% of all species went extinct, earning it the name "The Great Dying." Trilobites went completely extinct at this time, and over 95% of ammonite genera disappeared.
The cause was the "Siberian Traps," one of the largest volcanic events in history occurring in Siberia, but latest research paints an even more terrifying scenario.
The Complicity of Microbes and Nickel: Massive amounts of "nickel" released from the Siberian volcanoes rained down on the oceans, causing an explosive proliferation of "methanogens (a type of archaea)" that fed on it. The leading theory (the Rothman hypothesis) suggests that the methane gas they emitted caused far more severe global warming than the volcanic activity alone.
Furthermore, as magma burned through underground coal and rock salt layers, toxic halogen gases were generated, destroying the ozone layer. Powerful ultraviolet rays poured down on the surface, collapsing terrestrial forests and ecosystems. The Siberian lava covered an area 19 times the size of Japan, but its impact reached the opposite side of the Earth through chemical chain reactions, driving life into a corner.
The 4th - End-Triassic Mass Extinction
A synapsid (mammal-like reptile) that lived in the Early Triassic
About 201 million years ago, massive volcanic activity (CAMP: Central Atlantic Magmatic Province) accompanying the breakup of the Pangaea supercontinent occurred, resulting in the extinction of 76% of species. Traditionally, "global warming" was considered the main cause, but latest research (2024-2025) points out the importance of a "volcanic winter."
The volcanic activity did not continue sluggishly for millions of years, but occurred as intense pulses on a 100-year scale. While the Earth warmed due to the greenhouse effect of the initially released carbon dioxide, oxygen levels dropped, dealing a blow to large animals with high metabolic rates. The high temperatures dried up the watersides in the interior of the continents, depriving amphibian groups that lived there of their habitats.
Subsequently, sulfur aerosols formed by sulfur dioxide released by the volcanic activity reacting in the air blocked sunlight, subjecting the Earth to rapid cooling (winter). Dominant reptiles such as crocodilian ancestors (pseudosuchians) that had adapted to the tropics could not withstand this cold and went extinct.
On the other hand, the dinosaurs of the time, while still playing a supporting role, had already acquired feathers, enabling them to survive this sudden cold snap. Surviving the "one-two punch of cooling and heating," dinosaurs explosively diversified in a world without rivals, becoming the kings of the Jurassic period.
The 5th - End-Cretaceous Mass Extinction
Occurring about 66 million years ago. Dinosaurs, pterosaurs, marine reptiles, ammonites, and others went extinct, with 70% of species disappearing. For many years, the debate continued between the "asteroid impact theory" and the "Deccan Traps volcanic theory" of India, but decisive evidence was found in 2024.
Analysis of isotopes of the element "ruthenium" contained in the extinction layer revealed that its composition perfectly matched the components of a "carbonaceous chondrite (C-type asteroid)" that flew from far away, not from terrestrial volcanoes.
This confirmed that the direct trigger of the extinction was undoubtedly an asteroid impact. While the volcanic activity of the Deccan Traps also worsened the environment, it was the asteroid that delivered the final blow.
A species of ammonite that lived in the Cretaceous period. Sourced from France.
(*Note) Regarding the extinction timing of ammonites, there is no doubt they went extinct due to climate change from the asteroid impact, but fossils indicating they may have survived for tens to hundreds of thousands of years after the impact in some regions have also been found.
The 6th - The Currently Ongoing Mass Extinction
It is said that we are currently in the midst of the 6th mass extinction.
In the natural world, a "background extinction" normally occurs where about 10% of species go extinct every 1 million years. However, the current rate of extinction is said to be 1,000 times the natural state, and the number of endangered species reaches 49,505 (28% of all species).
The cause is due to the activities of us humans (Homo sapiens).
Latest statistical data highlights a different aspect from a simple "acceleration of extinction." Many recorded extinctions peaked in the early 1900s, and most of those were cases where endemic species on "islands" were driven to extinction by invasive species. This is considered the result brought about by the "introduction of invasive species" by humans.
The crisis we face today in the 2000s is that many organisms are in a state of "threat of extinction" due to "habitat destruction by humans" and "climate change triggered by human activities."
Research into past mass extinctions teaches us how fragile the Earth's systems are, and how it takes millions of years to recover once the balance is broken.