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Professor Andy TomkinsEarth and Planetary Sciences
Monash University
Abstract: All large planets in our Solar System have rings and Mars may have had a ring in the past. This raises the question of whether Earth also had a ring in the past. We examined the paleolatitudes of 21 meteor impact craters from an unusual period of enhanced cratering rate known as the Ordovician Impact Spike and found that all craters occur in an equatorial band at ≤30°, despite ~70% of exposed, potentially crater-preserving crust lying outside this band. Our statistical analysis indicates that it is highly unlikely - less than 1 in 25 million - that the observed crater distribution was produced by asteroids on orbits directly from the asteroid belt.
We propose that instead, a single large asteroid broke up due to tidal forces during a near-miss encounter with the Earth. The beginning of the Ordovician Impact Spike is marked by 466-million-year-old layers of sedimentary rock containing 100-1000 times more meteorite debris than normal, and we suggest that this represents the timing of the break up event.
Given the longevity of the impact spike and sediment-hosted meteorite debris accumulation, we suggest that a ring formed after this break up event, from which material deorbited to produce the observed crater distribution. We further speculate that shading of Earth by this ring may have triggered cooling into the Hirnantian global icehouse period.
Bio: Andy Tomkins is a petrologist and geochemist whose research covers a diverse range of geoscience subdisciplines. He completed a PhD in 2002 at the Australian National University, then an Alberta Ingenuity Fellowship at the University of Calgary in Canada, before moving to Monash University. There, he initially held a 5-year Monash Research Fellowship position and then gained a tenured position in 2010.
He won the Waldemar Lingren award in 2008 and the Silver Medal in 2021 from the Society of Economic Geologists. Andy particularly enjoys applying scientific principles that we’ve collectively learnt about the Earth to understand the evolution of Mars, the early Solar System, and asteroids.
Members and visitors are warmly invited to attend.
For further information visit: www.fieldgeologyclubsa.org.au
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Event Venue & Nearby Stays
Mawson Lecture Theatre, Adelaide,SA,Australia
