New research published in the journal Meteoritics & Planetary Science confirmed the extraterrestrial origin of a supposed meteorite crater in Northeast China’s Heilongjiang Province. With 1.85 kilometers in diameter and more than 300 meters deep, it is the largest impact on Earth in the last 100,000 years.
The southern third of the crater is missing, but other sections are well preserved, with a maximum elevation above the present crater floor of 150 meters. Scientists already suspected that the crescent-shaped hill in the densely forested area of the Xing’an mountains was a crater rim, but only a drillcore from the center of the structure revealed direct geological evidence for an impact origin.
The crater fill consists of a 110 meters thick succession of sediments deposited in a lake and later a swamp, underlain by a 319 meters thick layer of brecciated granite. The researchers think the bedrock was shattered into pieces by a powerful collision. Melted and recrystallized granite clasts suggest the rock was quickly heated to over 1,200 degrees and subsequently cooled in situ, consistent with an impact.
Petrographic investigations of unmelted granite clasts in the brecciated granite unit show the presence of shocked minerals – like quartz crystals with a distinct pattern of parallel, planar cracks, the result of shock waves traveling through the bedrock.
Named after the nearby city of Yilan, the Yilan Crater is estimated to have formed about 47,000 to 53,000 years ago, based on radiocarbon dates obtained from organic debris and soot found in sediment layers covering the shattered granite bedrock. Based on this young age, it is quite possible that the impact of the 100-meter-wide meteorite was witnessed by humans living in Siberia and Asia at the time.
About 190 confirmed impact craters were found so far on Earth. The oldest structures have an age of 2 billion years. Likely there were far more in the past, but erosion and tectonic activity destroyed many of them. The Moon alone is dotted with 30,000 craters. On Earth a few craters are believed to be still buried beneath younger sediments or ice caps, or hidden in the sea.
The famous Meteor Crater in Arizona was also created about 50,000 years ago, but is slightly smaller than Yilan Crater, with 1.2 km in diameter. Other “recent” impact craters on Earth are the 100 km wide Popigai Crater in northeast Siberia, the 85 km wide Chesapeake Bay in Virginia, both dated around 35 million years, and the 24 km wide Ries impact in Germany, dated to 14 million years. In 2018 the discovery of two approximately 30 km wide circular basins beneath Hiawatha Glacier, Greenland, was announced. Based on ice thickness and rates of ice erosion, the possible craters are estimated to be over 100,000 years old, but their impact origin remains unconfirmed. The only other confirmed impact crater in China is the Xiuyan Crater in Liaoning Province, with 1.8 km in diameter and unknown age.