One should not overestimate how much geography has changed during the human era. The largest differences are caused by the ice ages. The three last in particular I find interesting. Not only were they particularly cold. They were also contemporary with the current human species. Out species’ spread over the world has taken place during the latest.
Ice age has consisted most of the latest 300,000 years. They have only been interrupted by shorter interglacials. During these short periods it was about as warm as today. During the ice ages the entire world was both colder and dryer. But first and foremost the ice sheets took up very much water. In fact so much the seas sunk by up to 125 meters (410 feet). Periodically the Red Sea dried up because the strait to the south was blocked. The Mediterranean did not dry up since the Strait of Gibraltar is considerably deeper. In contrast the Black Sea was isolated. It did not dry up either because it mostly gets its water from rivers.
The English Channel formed at the peak of the last ice age. Before that Britain was connected to the mainland by an isthmus. During the ice ages the North Sea was dry to a higher or lesser degree. Rivers emptying into the North Sea then had their drainage between Britain and Denmark. At the peak of the last ice age they were blocked by ice sheet. The water level rose in the North Sea until it flowed over in the southwest. The forward-rushing water formed a river valley which became their new outlet. When the seas later rose the river valley was flooded. Since then the sea has worn on the English Channel’s coasts.
Also in other parts of the world islands were connected to the mainland. Java and Sumatra were fused to the present-day Malacca Peninsula. Borneo was periodically fused to them. In the same way New Guinea and Tasmania were fused to Australia. In contrast Australia was never connected to Asia. If it had large animals common in Southeast Asia would have spread to Australia. No-one was found there before they were taken there by humans.
Japan was also fused to East Asia’s mainland. The Sea of Japan has periodically been isolated from the Pacific. Like the Black Sea it got water from rivers emptying into it so it did not dry up. Maybe more interesting is the Bering Strait being dry. Cold-adapted animals could get across from the Chukchi Peninsula to Alaska. The way eastwards from Alaska was at the same time blocked by ice. Before they could spread further they were as such stuck in Alaska.
First and foremost the landscape was reshaped in areas which were ice-covered. Most of North America’s Great Lakes have formed this way. Before that there were a couple of lakes where Lake Superior is now. I think Lake Ontario is older since it is so deep. The rest have been shaped by the ice sheet as well as Lake Winnipeg, Great Slave Lake and Great Bear Lake. Here in Northern Europe a row of lakes and bays have formed in the same way. These include Vänern, Mälaren, the Gulf of Finland, Lake Ladoga, Lake Onega and the White Sea. I also think the Danish straits and the Sound were carved out by glaciers. Not to speak about all the fiords.
The weight of up to 4 kilometres (2½ miles) of ice has squished down the ground it laid on. The interior of the East has compensated for this by squishing up surrounding areas. When the ice melted away the Earth’s crust has started to return back in both these cases. Most of what has been ice-covered for this reason now has positive rebound. Areas around the borders of the ices instead have negative rebound. The result is the shape of coastlines has changed over millennia. The size and shape of lakes has changed too. Some has changed outlet over the course of millennia.
Other geological changes since the end of the last ice age have not been so drastic. Volcanic eruptions have created small islands or blasted such into pieces. In the same way volcanic eruptions has formed or blasted away peaks. Sandbars has eroded away and turned peninsulas into islands. Rivers have changed their course but only on the lowland.
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