Trinity College Dublin geologists found strong evidence that one of the largest preserved impact structures on Earth was caused by a comet and not a meteorite

DUBLIN, 18-11-2014 — /EuropaWire/ — Collaborative research led by geologists at Trinity College Dublin has found strong evidence that one of the largest preserved impact structures on Earth was caused by a comet colliding with our planet over 1.8 billion years ago.

The findings of this ancient impact are particularly topical with the current mission to provide more information about comets successfully relaying images of Comet 67P to the European Space Agency. A critical aim of the mission was to test whether the terrestrial hydrosphere was delivered by comets to an originally dry Earth.

In a recently published study in the international journal Terra Nova, the Trinity-led geologists explain the rationale behind their assertion that the Sudbury Basin in Ontario, Canada, was caused by a comet – and not a meteorite; comets are composed by dust and frozen gas and carry few heavy elements, whereas meteorites are solid rocks that delivered iron-loving elements, such as platinum, to a younger Earth.

By conducting geochemical analyses of the siderophile (iron-loving) elements found in and around the crater fill – and by modelling the impact with computer software – the geologists showed that whatever crashed to Earth was almost completely vaporised on entry. A meteorite of sufficient size to create a crater as large as the Sudbury Basin should only be partially vaporised on entry, which leaves a ‘comet-as-culprit’ scenario as by far the most likely.

Professor of Geology and Mineralogy in the School of Natural Sciences at Trinity, Balz Kamber, said: “Our findings provide further evidence that some very large terrestrial impact basins were created by comets, which is important and interesting in the context of the early bombardment of our inner Solar System – it might well be that comets were responsible for bringing volatile elements to the young Earth.”

He added: “Our geochemical evidence supports, in principle, the idea tested by the recent mission to comet 67P. Namely, we now have confidence from the geological record that the Earth was indeed hit, at least once, by a large comet that deposited its water into our hydrosphere.”

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