Russian Meteorite Spurs Interest in Geo-Space History — U.S. Midwest Phenomena Show Impact of Ordovician Mega-Event?
February 20, 2013 • 11:36AM

Since the Russian meteorite hit, questions of geo-space history are now getting popular attention, as part of the upsurge of alarm and excitement over the threat of objects striking Earth.

In coverage today, the work of two groupings of geoscientists, on Midwest phenomena, is reported. They are analyzing craters and meteorite debris in Iowa, Wisconsin, and nearby, in terms of apparent evidence supporting the current view that there was a "Period of Heavy Bombardment," of objects hitting Earth, in the Middle Ordovician period, around 470 million years ago. It is theorized that, at this time period, a gigantic asteroid collided with another body in space beyond Mars, and debris rained down on Earth, including on the Moon. A density of craters and rock phenomena have been analyzed as dating to this period. It is of note that the first of the "Five Mass Extinctions" is dated to the O-S, or Ordovician-Silurian Extinction Event, in the 450-440 million years ago period.

In Wisconsin, a description was published today on the University of Wisconsin website, about results of refined geochemical analysis which has been done on several pounds of meteorite debris which hit ground in an April, 2010 fireball event in the southwestern part of the state, near the town of Mifflin. The rocky material is what's called L5 chondrite, one of the most common types of meteorite, which are considered descendents from the same parent asteroid of the mega-collision theory. The Wisconsin article gives a summary history, of the mega-asteroid being "one astronomical body that coalesced in the solar system 4.56 billion years ago, even before the Earth came together from the primordial dust that formed the rocky inner planets." ("Secrets of Wisconsin Meteorite Revealed," by David Tenenbaum, Feb. 19, www.news.wisc.edu).

What happened next in this history, as summarized by UW-Madison geoscientist John Valley, is that much later, around 470 million years ago, "the parent asteroid of L5 chondrites was destroyed, probably by a large impact with another body." The Earth was bombarded by L Chondrites. Valley said, "There are limestone quarries where black rocks can be seen in the white limestone. There are meteorites, and we can date their arrival to 470 million years ago. We never find them older than 470 million years, and after about 10 million years, they become rare."

In Iowa, there is a newly-identified impact-crater, located under the town of Decorah (northeast part of the state), whose rock strata, underlying newer layers of shale, place the formation in the mid-Ordovician time frame of "Heavy Bombardment." Moreover, there are two other craters considered as being around the same age, and along the same alignment as the Decorah crater — the Rock Elm crater in Wisconsin, and the Ames crater in Oklahoma. This provokes speculation on whether there was one mega-meteorite event involved in these multiple craters. Today's Washington Post story, headlined "Crate Yields Smashing Hints," summarizes the geochemical reports on the rocks, showing that, the "impact is believed to be 470 million years old."