...Earth was bombarded on a regular basis during its formative years -- by meteorites and other space rocks. Some of those collisions left behind evidence that is still observable today in the form of craters. One of them is Mistastin Lake crater located in Labrador Canada, which is approximately 28 kilometers across, suggesting that the object that struck the Earth there was large. The researchers dated the collision that caused the crater back to approximately 38 million years ago... In studying the crater, the researchers found evidence of zircon, a common mineral, being changed into cubic zirconia. Prior work with...