Dr. John Percival spent his career at the Geological Survey of Canada (GSC) studying the Canadian Shield in remote parts of northern Quebec, Ontario, Manitoba, and Nunavut. He is published in over 300 journal articles, reports, maps, book chapters and books. John continues his research as an emeritus scientist at the GSC.
Objects from outer space! Meteorites have fascinated scientists since their recognition in 1803.
Although there is an almost continuous rain of interplanetary dust, regular meteorite showers and occasional fireballs entering the atmosphere, only rarely do objects large enough to excavate craters strike the Earth.
The effect can be catastrophic when they do. About 66 million years ago, a 10-15 km diameter meteorite travelling at 10 km/second struck the Yucatan Peninsula in present day Mexico, vaporizing rocks within a 150-km wide, 20-km deep crater. Rock vapour enveloped the globe, resulting in the extinction of about half of Earth’s species, including the dinosaurs. This crater, called the Chicxulub Crater, is now covered with sediments and seawater.
But the Chicxulub event was not the worst mass extinction: that occurred 250 million years ago when about 90% of species disappeared.
The distinction for the largest visible impact crater belongs to the 2.02 billion-year-old, 300-km diameter Vredefort structure of South Africa. A still larger impact crater (Mars-sized) is thought to be responsible for striking the primitive Earth, ejecting material that became the Moon about 4.53 billion years ago.
The talk will present an illustrated tour of impact events, including notable Canadian craters: the closest one (450-million-year-old Brent crater in eastern Algonquin Park); the most obvious one (1.4 million-year-old Pingualuit crater of northern Ungava); and the richest one (1.85 billion-year-old Sudbury structure).
Dr. John Percival who received a B.Sc. in geology from Concordia University and Masters and Doctorate degrees in geology from Queen’s University, spent his career at the Geological Survey of Canada (GSC) studying the Canadian Shield in remote parts of northern Quebec, Ontario, Manitoba, and Nunavut. He is published in over 300 journal articles, reports, maps, book chapters and books.
He also served as an adjunct professor (U. Ottawa), on the editorial boards of three international journals, and took a leadership role in Lithoprobe, Canada’s national geoscience program from 1982 to 2002. The Lithoprobe project built a trans-continental 3-D geologic knowledge framework.
John delivered speaking tours at universities across Canada in 1990 and 2001 as Distinguished Lecturer of the Geological Association of Canada, and in 2017 was awarded the Gold Medal of the Professional Institute of the Public Service of Canada.
John continues his research as an emeritus scientist at the GSC.