Why Did The 'Great Dying' Last for Five Million Years? Science May Finally Have The Answer

The Great Dying has remained a captivating topic for experts. However, some aspects of this event remain under wraps for scientists, according to Discover Wildlife. One of them being, why did the horrendous phenomenon last for five million years? The event occurred around 250 million years ago and caused absolute havoc with the death of a whopping 81 percent of marine species and 70 percent of vertebrate terrestrial animals. Insects and plants could also not escape the terror and took heavy losses. Several causes have been proposed, but the event's sustenance has remained a source of debate. A possible reason for the Great Dying's longevity has been explained in the journal Nature.

The 'Great Dying'

Scientists believe that the Great Dying happened due to an increase in volcanic activity, which took place in present-day Siberia. The eruptions led to the creation of a massive lava plain that came to be known as the Siberian Traps. The lava plain fired up the oil and coal reserves and released tons of methane gas. The surroundings got filled with sulphur dioxide, methane, and atmospheric CO2, which tore apart the ozone layer. It led to the arrival of tons of solar radiation on the surface, which acidified the oceans in the world. The damage was global and continued for five million years, during which several beings died at an unprecedented rate. 

As per estimates, the carbon dioxide emissions from molten rocks lasted between 50,000 and 500,000 years, as reported by The Conversation. This emission caused an increase in the carbon dioxide content and temperature of the atmosphere. The Earth grew hotter by 6°C to 10°C, a sudden change that could not be adapted to by the majority of the living beings. Both of these changes were the primary trigger that instantaneously killed most life at that time. Scientists were shocked by the 'Great Dying' as the consequences of such emissions should last for 100,000 to a million years. After that, the climate system should return to 'normal', but in this case, the 'super greenhouse conditions' persisted for five million years. 

Reason for Persistence

Researchers believe the loss of forest cover caused the event to last for five million years. They analyzed the fossil record of a variety of land plant biomes, such as tropical, subtropical, arid, temperate, and scrub, and tried to understand how they changed from before the mass extinction event to eight million years after it. The team concluded that due to a rapid increase in temperature, low- to mid-latitude vegetation dried rapidly, particularly the rainforests. It heavily impacted the carbon cycle in play within these forests. The amount of carbon absorbed by peat bogs and tropical and sub-tropical forests located around the equator has reduced considerably. 

The evidence shows that no biomes survived in the tropical regions after the mass extinction. They were replaced by tiny lycopods, which were not capable of storing as much carbon as their previous counterparts. The big trees maintained a hold in poles, mountainous regions, and coastal areas, but took five million years to repopulate the Earth. During this period, the Earth's temperature remained upwards of 34 °C. It was only after this repopulation that the temperature started to come under control with rejuvenation of the carbon cycle, and the 'Great Dying' came to an end. This replacement of large trees with small plants can also be seen in the present-day Australian Outback and may cause the same carbon cycle issues, as it did after the Great Dying. 

Relation to Modern Times

Researchers believe that the findings are a stark warning of what could happen if humans continue to treat rainforests as they have in recent times. "A key implication of our work, however, is that life on Earth, while resilient, is unable to respond to massive changes on short time scales without drastic rewirings of the biotic landscape," Zhen Xu, the lead author of the study, shared.