Charcoal from a hearth site in Utah, 2,500 miles south of Alaska, is known to be 10,500 years old. Researchers concluded that, since glaciers blocked human migration south from the Alaska-Siberia land bridge between 17,000 and 10,000 years ago, humans must have arrived in the Americas more than 17,000 years ago.

Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?