3) Large meteorites strike Earth sufficiently frequently to explain the extinction record. Eugene Shoemaker demonstrated a strong relationship between frequency and size of impacts. A 10km bolide should strike the Earth once every 100 Ma. In 1908 a small comet probably exploded over Tunguska Siberia.
{"Image DocumentName": "3) Large meteorites strike Earth sufficiently frequently to explain the extinction record. Eugene Shoemaker demonstrated a strong relationship between frequency and size of impacts. A 10km bolide should strike the Earth once every 100 Ma. In 1908 a small comet probably exploded over Tunguska Siberia.", "Image ImageDescription": "4) On shorter time scales, such events should be rare. In polarity chron C29R, there are no other iridium enrichments. The 34 million year sandwich around the K-T boundary has no other anomalies. In fact it is by far the biggest anomaly of geologic time.", "Image XResolution": "37", "Image YResolution": "37", "Image ResolutionUnit": "Pixels/Centimeter", "Image Software": "SlidePlayer", "Image YCbCrPositioning": "Centered"}