Professor Zhang: the prehistoric essential tools found in South America existed 13,000 years ago. Some archaeologists believe that these tools were used by people whose ancestors migrated from Siberia to Alaska. This view is untenable. In order to reach South America, these people had to trek 13, 000 years ago, and 13, 000-year-old wooden tools were never found between Alaska and South America. Researcher Li: I'm afraid you've overlooked: these wooden tools are found in peat bogs, which are rarely found in North America. Wooden tools rot and dissolve in ordinary soil within a few years.
The problem discussed by Professor Zhang and researcher Li is whether it is possible for these people to complete the long journey from Alaska to South America by 13,000 years ago.