Assistant project coordinator for petroleum geology at the Illinois State Geological Survey (ISGS) Charles Monson recently published a study revealing a possible link between a meteorite impact crater found in Illinois and a 93-mile-wide asteroid called the L-chondrite parent body (LCPB) that broke apart 466 million years ago. Some scientists now suspect that this asteroid breakup triggered a larger event that drastically altered the course of evolution on Earth.
Well, in short, it was a bad day for Peoria County about 450 million years ago. A meteorite bigger than the State Farm Center hit near the present-day Village of Glasford, a little ways southwest of Peoria. It created a 2.5-mile-wide crater that we now call the Glasford structure. This was one of only two meteor craters in Illinois that we know about, out of 200 worldwide.
You said this is one of two meteor impacts in Illinois, where is the other impact located?
The other one is in the Des Plaines area, very near O’Hare airport.
How did ISGS find out about the crater?
It was actually first identified in 1963. It is buried 1,150 feet underground and we only know about it because Ameren drilled into the center of the crater and found lots of shattered, distorted, and displaced rock. A few decades later, ISGS scientists and colleagues reported shatter cones from Glasford, which only form in a nuclear blast or a meteorite impact. We found and documented additional shatter cones, confirming the meteorite impact origin of the structure.
How do you know when it hit Peoria County?
We know that 450 million years ago, most of Illinois was underwater. The crater was quickly filled with marine sediments and fossils, which give us clues to when this event took place. Inside the crater, we found fossils of graptolites, which are extinct now but were widespread in the ocean at that time. Graptolites evolved quickly and we know which species existed at specific times in geologic history, so identifying the graptolites in the crater fill lets us determine the age. We also found shells and pieces of sea scorpions (eurypterids), which have been found in an Iowa meteor crater as well. While the impact definitely caused a lot of destruction, the marine deposits indicate that life got back to normal shortly after this event - it is truly a testament to how life rebounds.
What does this mean for your individual work and your field of study?
The results of my study indicate that the Glasford impact was probably connected to a global event called the Great Ordovician Meteorite Shower (GOMS), when Earth was bombarded by meteorites formed by a massive collision in the asteroid belt about 466 million years ago. This collision created a new family of meteorites spread out across the solar system in the later part of the Ordovician Period. We would need additional data, such as extraterrestrial chromite in the crater fill, to prove a connection to GOMS--and we are currently working on that! But the timing of the impact is strong circumstantial evidence of a connection.
New research by Dr. Birger Schmitz, of Lund University and the Field Museum, suggests that large amounts of dust from the disintegrated asteroid also entered the Earth’s atmosphere, triggering the mid-Ordovician Ice Age. This drastically changed the course of evolution and may have caused some species to become extinct, but according to Schmitz’s hypothesis, it also spurred new species to evolve as life adapted to changing conditions.
Both studies are complementary. They both examine the effects of material from the destruction of the LCPB asteroid reaching Earth. Their study focuses on the large amounts of extraterrestrial dust that arrived shortly after the event and the related global biodiversity changes.
My study relates to the larger asteroid pieces that hit Earth in relatively large numbers for about 30 million years after the event, creating local catastrophes. More specifically, my work reveals that the Glasford crater is probably a product of the GOMS event and based on fossils that we found in the marine rocks within the crater, we can also note the effects of the impact on prehistoric creatures in Illinois, complementary to Dr. Schmitz’s discussion of global biodiversity changes due to the dust-induced ice age.
The Illinois State Geological Survey is a division of the Prairie Research Institute at the University of Illinois.