Lake Agassiz

I've been reading a book called "Ancient Shores" which is a story about a strange boat found in North Dakota. Apparently 14 thousand years ago a chunk of north america was under water, covered by Lake Agassiz. The book got me thinking. 14 thousand years ago ISNT that long ago. How much of human history are we missing due to it being covered up by planetary changes ? The planet has changed soooo much ~recently~ and no one really talks about it. How different was the world map 10000 years ago? I'm sure there was more changes than this lake...