Saturday, June 30, 2012

Impact Craters

The moon and the earth were bombarded by many large and small meteorites and comets during the first 500 million years of the Solar System.
Gosses Bluff impact crater
in Northern Territory, Australia

The earth has about 180 identified impact craters. In contrast, the remains of thousands of impact craters are visible on the moon.

The moon's surface is comparatively static, while earth's surface is an ever-changing system with plate tectonics, mountain formation, and erosion.

Over geological time, most of earth's impact craters are:
  • Eroded away;
  • Obliterated by mountain building;
  • Buried by younger deposits; or
  • Inundated by oceans and fresh water.
Greenland's Maniitsoq Crater

Discovery in Greenland

The remains of a 3000 million year-old meteorite impact was discovered on the western coast of Greenland in 2009 by a GEUS geologist. The crater impact structure found near the town of Maniitsoq is about 310 miles wide.

Until the discovery of the Maniitsoq impact crater, the 2020 million year-old, 186 miles wide Vredefort crater in South Africa was believed to be earth's oldest (and largest) impact structure.

The oldest identified impact craters are shown in the table below:

Name Location Diameter
(million years)
Maniitsoq Western Greenland 310 3000
Vredefort South Africa 186 2020
Yarrabubba Western Australia 19 2000
Sudbury Ontario, Canada 155 1850
Keurusselkä Western Finland 19 1800
Amelia Creek Northern Territory, AU 12 1660-600
Shoemaker Western Territory, AU 19 1630
Strangways Northern Territory, AU 16 646
Beaverhead Idaho / Montana, US 37 600
Acraman South Australia 56 590
Facts which at first seem improbable will, even on scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty.
~ Galileo Galilei