The dinosaurs were already having a hard time before an asteroid smashed into Earth and finished them off.

Scientists have said that huge volcanic eruptions may have contaminated the planet with deadly mercury before the space rock hit our planet.

A team from the University of Michigan analysed fossiled marine mollusc shells and found increased mercury levels.

It’s believed this dangerous substance was produced during the formation of the Deccan Traps – a massive volcanic formation in India.

These eruptions began before the impact and lasted ‘on and off’ for a million years.

The mollusc shells showed the same level of mercury pollution as modern clam shells collected in sites of industrial pollution in Virginia.

‘For the first time, we can provide insights into the distinct climatic and environmental impacts of Deccan Traps volcanism by analyzing a single material,’ said Kyle Meyer, lead author of the new study.

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‘It was incredibly surprising to see that the exact same samples where marine temperatures showed an abrupt warming signal also exhibited the highest mercury concentrations and that these concentrations were of similar magnitude to a site of significant modern industrial mercury contamination.’

Mercury is a toxic trace metal that ‘poses a health threat to humans, fish and wildlife’.

Today, it’s generated by coal-fired power plants and gold mines.

At Virginia’s South River, where the researchers collected freshwater clamshells, there are signs which warn residents not to eat fish from the river.

‘The modern site has a fishing ban for humans because of high mercury levels. So, imagine the environmental impact of having this level of mercury contamination globally for tens to hundreds of thousands of years,’ said geochemist and study co-author Sierra Petersen, who was Meyer’s co-adviser.

The Deccan Traps eruptions formed much of western India and were centred around the time of the Cretaceous-Paleogene (K-Pg) mass extinction, which took place 66 million years ago and spelt doom for the dinos.