The Great Dying, which struck the Earth a quarter of a billion years ago, claimed more lives than any other mass extinction in the planet's history.

The most popular theory for its cause is volcanic eruptions that led to immense amounts of basalt lava spreading across Siberia over a period of 600,000 years.

Now, evidence of vinegar-like acid rain caused by the sulphur dioxide in these eruption has been found by researchers scouring 250 million-year-old rocks in Italy.

In an attempt to explain how vanillin could exist in the rocks for so long, the researchers turned to the dairy industry, which sometimes uses vanilla in milk.Acidifying the milk protects vanillin as the low pH deactivates the enzymes that would break it down. The same can be said for vanillin in ancient rock

'For the first time, we can say that soils from this time had an acidity similar to that of vinegar,' Mark Sephton, a geologist at Imperial College London told Smithsonian.com.

The rocks in Italy's Vigo Meano contained vanillin – the substance that gives vanilla its distinct taste and flavour. The discovery was a surprise, as vanillin is usually broken down by bacteria.

In an attempt to explain how vanillin could exist in the rocks for so long, the researchers turned to the dairy industry, which sometimes uses vanilla in milk.

The rocks provide further evidence to suggest the Great Dying was triggered by massive volcanic eruptions that spewed out of sulphur dioxide that in turn caused acidic rain

Acidifying the milk protects vanillin as the low pH deactivates the enzymes that would break it down. The same can be said for vanillin in ancient rock.

OTHER EXPLANATIONS FOR THE GREAT DYING A huge impact event has been suggested as a possible cause of the mass extinction, based on the examination of grains of 'shocked quartz' and meteorite fragments in Antarctica, but no impact site has been found. One of the attractions of the theory is that it could trigger other causes such as the Siberian Traps eruptions. Widespread ocean anoxia (a severe deficiency of oxygen) has also been blamed for the event in the Late Permian to the Early Triassic. The spread of toxic, oxygen-depleted water would have been devastating for marine life, producing widespread die-offs. Models of ocean chemistry show that anoxia and euxinia (the presence of hydrogen sulphide) would have been closely associated with high levels of carbon dioxide, which suggests a combination of gases acted as a killing mechanism. Advertisement

'Our data fits the idea that acid rain caused the microbes to cease functioning,' says Henk Visscher, a paleoecologist at Utrecht University in the Netherlands.

The findings follow a similar study in 2013 by US scientists who simulated the Great Dying.

The MIT researchers found that sulphur emissions from massive volcano eruptions were significant enough to create extremely acidic rain, which could have affected plant growth.

They believe such acidity may have been sufficient to disfigure plants and stunt their growth, contributing to their ultimate extinction.

'Imagine you're a plant that's growing happily in the latest Permian,' said Benjamin Black, a postdoctoral researcher in MIT's Department of Earth, Atmospheric and Planetary Sciences.

'It's been getting hotter and hotter, but perhaps your species has had time to adjust to that.

But then quite suddenly, over the course of a few months, the rain begins to sizzle with sulphuric acid. It would be quite a shock if you were that plant,' he said.

After the eruptions ended, the researchers found believe pH levels in rain bounced back, becoming less acidic within one year.

The rocks in Italy's Vigo Meano contained vanillin – the substance that gives vanilla its distinct taste and flavour. The discovery was a surprise, as vanillin is usually broken down by bacteria

EARTH'S 'BIG FIVE' MASS EXTINCTION EVENTS Meteor impacts contributed to wiping out species during mass extinction events on Earth Ordovician-Silurian mass extinction - 443.4 million years ago This was the third largest extinction in Earth's history, and had two peaks of dying separated by hundreds of thousands of years. Around 26 per cent of all marine families were wiped out and 60 per cent of all genera - an estimated 82-88 per cent of all species. Late Devonian mass extinction - 375-359 million years ago Three quarters of all species on Earth died out in the Late Devonian mass extinction, though it may have been a series of extinctions over several million years. Around 22 per cent of all marine families, and 57 per cent of all genera were wiped out - an estimated 79-87 per cent of all species. Permian mass extinction - 252 million years ago The Permian mass extinction has been nicknamed The Great Dying, since an incredible 96 per cent of species died out. All life on Earth today is descended from the 4 per cent of species that survived. Triassic-Jurassic mass extinction - 201 million years ago There were two or three phases of extinction that made up the Triassic-Jurassic mass extinction event. 22 per cent of all marine families and 53 per cent of all genera - an estimated 76-84 per cent of all species. Cretaceous-Tertiary mass extinction - 66 million years ago The Cretaceous-Tertiary mass extinction was the event that wiped out the dinosaurs. However, many other organisms perished including 16 per cent of all marine families and 47 per cent of all genera - an estimated 71-81 per cent of all species. Advertisement



