<human>:  What caused the K-T mass extinction?
<bot>: The K-T extinction was caused by a massive asteroid impact. The impact wiped out the dinosaurs and many other species. The asteroid was about 10 kilometers wide and it hit Earth at a speed of about 30 kilometers per second. The impact caused a huge amount of dust and debris to be thrown into the atmosphere, which blocked out the sun and caused temperatures to drop. This caused the extinction of many species.