Scientists have found evidence for a massive impact crater hidden underwater near the Falkland Islands. If confirmed, it could be the second biggest crater on Earth – and perhaps linked to our planet’s greatest extinction event.

The discovery was led by Max Rocca from Argentina’s Planetary Society. The researchers estimate the crater may be 250 kilometers (155 miles) in width and 270 to 250 million years old. The findings are published in the journal Terra Nova.

Its existence was inferred by noticing a decrease in the strength of Earth’s gravity over a section of the Atlantic Ocean. This may be the result of younger low-density material from an impact filling the basin.

They also found an increase in Earth’s magnetism at the site, which is a characteristic of large impact structures such as the 66-million-year-old Chicxulub impact crater in Mexico. Previous research suggested this may have been due to volcanic activity, but the researchers argue if that was the case, the gravity readings would be the opposite to what they observed.

“The presence of a large, buried impact structure, however, can explain the occurrence of both a negative gravity anomaly and a positive magnetic anomaly in the same area,” they write.

^{The crater is at S 51º 00’, W 62º 00’. Google Maps}

If the crater is confirmed as being from the Late Paleozoic era, the researchers also suggest it may be linked to the biggest extinction event in history, the Great Dying, which occurred about 252 million years ago.

More than 90 percent of species on Earth were wiped out at this time, with a number of possible causes including volcanic activity, draining of oxygen in the oceans, and extreme climate change. There have been suggestions an impact played a part, too, but no crater had been found.

"If the proposed crater turns out to be 250 million years old, it could correlate with the largest mass extinction ever – the Permian extinctions, which wiped out more than 90 percent of all species," study co-author Michael Rampino from New York University said in a statement.

They argue that future drilling in this basin “is a must”, with no drilling yet being performed here. Like Chicxulub, there is no actual visible crater in submarine maps of the area, so indirect evidence for the crater is essential.

The largest known crater on Earth is the Vredefort crater in South Africa, which measures about 300 kilometers (190 miles) across and dates back 2.02 billion years. This Falklands crater would tie for second with the Sudbury crater in Ontario, Canada, which also measures 250 kilometers (155 miles) across and is about 1.85 billion years old.