Chesapeake Bay Crater Montgomery College Planetarium at Takoma Park/Silver Spring By Dr. Harold Williams http://montgomerycollege.edu/Departments/planet/
Synopsis • 35.5 ± 0.6 million years ago, when Washington, DC and Richmond VA were on the coast, (sea level was higher then) • an object hit the earth on the continental shelf in the Atlantic ocean, N 37° 17' W 76° 1', • causing a crater 85 km in diameter. • After sea level fell, this crater would help form the Chesapeake Bay. • The impact site is now called the lower Chesapeake Bay in Virginia.
Where did this information come from mostly. Who did most of the real work and research. http://woodshole.er.usgs.gov/epubs/bolide/index.html Principal Investigator C. Wylie Poag firstname.lastname@example.org
Bolide? • Extraterrestrial body in the 1-10 km size range • Impacts the earth at velocities of 20-70 km/sec = Mach 75
Earliest identified crater on Earth • Some Links • Meteor Crater http://www.meteorcrater.com/ • Barringer Crater http://www.barringercrater.com/
Complex Craters Manicouagan, Quebec Canada, 70 km (43.4 miles) across, Formed around 212 million years ago, Lake surrounds the more erosion-resistant melt sheet created by the impact onto metamorphic and igneous rocks on the stable Canadian craton.
Some Shocked Quartz • PDF, Planar Deformation Features, Link http://www.unb.ca/fredericton/science/emunit/Trepmann/Shocked%20quartz.html
S-1 Large shocked quartz grains with planar deformation features (PDFs) identified in the Fraser Park, Sydney Basin Permian-Triassic boundary layer. Inset in upper photo shows close-up of intersecting PDFs. Quartz grains are mounted in oil and photographed in plane polarized light.
Radiometric ages in tektite glass • This age was confirmed by determining the ratio of two isotopes of argon gas contained in the tektite glass. • 35.5 ± 0.6 million years ago
Summary • During the late Eocene, the formerly quiescent geological regime of the Virginia Coastal Plain was transformed when a bolide struck in the vicinity of the Delmarva Peninsular
Produced the following principal consequences: • The bolide carved a roughly circular crater twice the size of the state of Rhode Island (~6400 km2), and nearly as deep as the Grand Canyon (1.3 km deep). • The excavation truncated all existing ground water aquifers in the impact area by gouging ~4300 km3 of rock. • Structural and topographic low formed over the crater. • The impact crater may have predetermined the present-day location of Chesapeake Bay. • A porous breccia lens, 600-1200 m thick, replaced local aquifers, resulting in ground water ~1.5 times saltier than normal sea water.
2004MN4 now 99942 Apophis • Link http://en.wikipedia.org/wiki/2004_MN4 • Friday, April 13, 2029 near miss of 320 m 4.6×1010 kg asteroid • Magnitude 3.3 moving at 42 degrees/hour maximum angular speed with a diameter of 2 arc seconds from Europe and Africa • Change from Aten to Apollo