Complex sentence: They appear to have evolved in Alaska from people using the Arctic small tool tradition who probably had migrated to Alaska from Siberia at least 2,000 to 3,000 years earlier, though they might have been in Alaska as far back as 10,000 to 12,000 years or more.
Split into simpler sentences: They appear to have evolved in Alaska from people using the Arctic small tool tradition. They probably had migrated to Alaska from Siberia at least 2,000 to 3,000 years earlier, though they might have been in Alaska as far back as 10,000 to 12,000 years or more.