Anthropology

dating indicate a much longer time for people in the Americas than the old Clovis theory originally suggested (11,000 years ago). How much longer? Depends on who you ask. Most estimates that I've seen suggest at least 20,000 years ago. Probably more, IMO.

I don't buy the Clovis theory of the first people entering America only by land at Beringia, and then the interior of North America only when an ice free corridor opened up. Humans reached Australia by boat at least 50,000 years ago.

Beringia did not form overnight. As more land gradually was exposed, people who were adapted to a coastal marine life probably followed the coastlines. They could have bridged the gap between Asia and North America by boat at a much narrower Bering Strait before the two continents were fully connected. Or, they could have followed the Aleutian Islands since they were connected to each other and almost to the Kamchatka Peninsula in Asia, which in turn was connected to islands leading to Japan when glaciation exposed and connected more land. This would have been farther south of the Arctic region.

I think the earliest people entering N.America came by boat. Some continued down the Pacific coastline. Others followed rivers, streams, and lakes inland, south of the glaciers, where melt runoff provided abundant sources of food and fur animals at watering sites. Meadowcroft Rock Shelter in southwest PA is an example of such a place, dating back to 14,000 years ago and likely (but disputed) earlier dates at lower layers.

The earliest people could have arrived as far back as 30,000 years ago, although there is no accepted evidence of that, yet.

Regarding trade with eastern Russia and the rest of east Asia, maybe it happened between Alaska, the Pacific Northwest, and Asia. There is some genetic evidence of "backflow genes" in that region. But not beyond that area.

No evidence of those early Americans riding horses. Horses originated in America and were hunted along with other mammals by humans. Those early horse forms were not like the ones tamed for riding thousands of years later in Asia. Horses migrated into Asia across Beringia before the glaciers melted, and evolved further on the open Asian steppes before becoming tamed for riding. By the time of Columbus, all horses were extinct in the Americas and were brought here by Europeans.