Dr. David Gwynn

There's two major ice sheets in North America. There's the Laurentide ice sheet, which extends from what's present-day northern North America down to Central Ohio. I don't know if that's going to work for all of your audience, but basically past the Canadian-US border. Yes.

There's two major ice sheets in North America. There's the Laurentide ice sheet, which extends from what's present-day northern North America down to Central Ohio. I don't know if that's going to work for all of your audience, but basically past the Canadian-US border. Yes.

There's two major ice sheets in North America. There's the Laurentide ice sheet, which extends from what's present-day northern North America down to Central Ohio. I don't know if that's going to work for all of your audience, but basically past the Canadian-US border. Yes.

And it goes from Newfoundland and Labrador all the way across Canada and laps up against the eastern flank of the Rocky Mountains. That's one big ice sheet, and it's literally kilometers thick. On the other side of the Rocky Mountain spine, you've got the Cordilleran Ice Sheet. And these are a series of mountain glaciers that come down from high elevation and coalesce to form an ice sheet.

And it goes from Newfoundland and Labrador all the way across Canada and laps up against the eastern flank of the Rocky Mountains. That's one big ice sheet, and it's literally kilometers thick. On the other side of the Rocky Mountain spine, you've got the Cordilleran Ice Sheet. And these are a series of mountain glaciers that come down from high elevation and coalesce to form an ice sheet.

And it goes from Newfoundland and Labrador all the way across Canada and laps up against the eastern flank of the Rocky Mountains. That's one big ice sheet, and it's literally kilometers thick. On the other side of the Rocky Mountain spine, you've got the Cordilleran Ice Sheet. And these are a series of mountain glaciers that come down from high elevation and coalesce to form an ice sheet.

And that extends from the western edge of the Rocky Mountains down to the Pacific coast. So you've walked across from Asia, Siberia into Alaska, but then you're going to have to stop because you've got those two big ice sheets between you and the rest of North America.

And that extends from the western edge of the Rocky Mountains down to the Pacific coast. So you've walked across from Asia, Siberia into Alaska, but then you're going to have to stop because you've got those two big ice sheets between you and the rest of North America.

And that extends from the western edge of the Rocky Mountains down to the Pacific coast. So you've walked across from Asia, Siberia into Alaska, but then you're going to have to stop because you've got those two big ice sheets between you and the rest of North America.

Yes, exactly. Good. Thank you. I should have clarified that. Yeah. Alaska is a cul-de-sac. as it were, right? It's a dead end. You can get into Alaska because Alaska was glaciated along the Aleutian Islands and in Southern Alaska, it was glaciated on top of the Brooks Range in sort of Northern Alaska, but otherwise it was ice-free, okay?

Yes, exactly. Good. Thank you. I should have clarified that. Yeah. Alaska is a cul-de-sac. as it were, right? It's a dead end. You can get into Alaska because Alaska was glaciated along the Aleutian Islands and in Southern Alaska, it was glaciated on top of the Brooks Range in sort of Northern Alaska, but otherwise it was ice-free, okay?

Yes, exactly. Good. Thank you. I should have clarified that. Yeah. Alaska is a cul-de-sac. as it were, right? It's a dead end. You can get into Alaska because Alaska was glaciated along the Aleutian Islands and in Southern Alaska, it was glaciated on top of the Brooks Range in sort of Northern Alaska, but otherwise it was ice-free, okay?

So you walk across the land bridge, you get into Alaska and you're thinking, you know, you're checking your watch and you're thinking, I could be in Miami, Florida if I just keep moving, right? But no, you can't because the glacial conditions that produce that land bridge by reducing the sea level at the same time are an obstruction.

So you walk across the land bridge, you get into Alaska and you're thinking, you know, you're checking your watch and you're thinking, I could be in Miami, Florida if I just keep moving, right? But no, you can't because the glacial conditions that produce that land bridge by reducing the sea level at the same time are an obstruction.

So you walk across the land bridge, you get into Alaska and you're thinking, you know, you're checking your watch and you're thinking, I could be in Miami, Florida if I just keep moving, right? But no, you can't because the glacial conditions that produce that land bridge by reducing the sea level at the same time are an obstruction.

Now, what that means is that it sort of sets some general parameters for when people could have come in, because it basically means that if we're assuming that they walked across, and at this time period, that's the most likely scenario, they could either come in after the glaciers have started to expand and sea level has dropped at least 52 meters, and before it has, the ice sheets, that is, have completely obstructed the route south,

Now, what that means is that it sort of sets some general parameters for when people could have come in, because it basically means that if we're assuming that they walked across, and at this time period, that's the most likely scenario, they could either come in after the glaciers have started to expand and sea level has dropped at least 52 meters, and before it has, the ice sheets, that is, have completely obstructed the route south,

Now, what that means is that it sort of sets some general parameters for when people could have come in, because it basically means that if we're assuming that they walked across, and at this time period, that's the most likely scenario, they could either come in after the glaciers have started to expand and sea level has dropped at least 52 meters, and before it has, the ice sheets, that is, have completely obstructed the route south,

Or they have to wait until after the ice sheets begin to melt. Because when the ice sheets begin to melt as the world is warming at the end of the ice age, you've got a couple of routes that will open up that will take you from that cul-de-sac where you've been parked for however many centuries or millennia down into what we refer to here in the States as the lower 48, right? The lower 48 states.

Or they have to wait until after the ice sheets begin to melt. Because when the ice sheets begin to melt as the world is warming at the end of the ice age, you've got a couple of routes that will open up that will take you from that cul-de-sac where you've been parked for however many centuries or millennia down into what we refer to here in the States as the lower 48, right? The lower 48 states.