It took a very long time, millions of years, for the next transport mode - boats - to emerge. There is no way of knowing when boats were discovered, but it probably was 50 to 100,000 years ago, and likely coincided with the spread of humanity across the globe, as it came out of its ancestral home in Africa.

The first boats were probably simple logs, which evolved into rafts, canoes, kayaks and so on. Sails were added a few thousand years ago, and grew eventually into the mighty sailing ships of the 1700's and 1800's. As steam engines developed, sailing ships gave way to the modern engine powered ships we have today. Although ships continue to evolve, the improvements are marginal. Ships will continue to be limited in speed, with maximum capabilities of a few tens of mph. Ship capacities, already at the million deadweight ton level, are not likely to grow much larger.

The invention of the wheel was the next major breakthrough in transport. Again, we can only guess at the date that it occurred. It probably coincided with the development of agriculture and cities, sometime in the time period 5000 to 10,000 BC. It seems unlikely that hunter-gatherer groups would have much use for wheeled vehicles. The American Indians, for example, never did use wheeled vehicles, though they had wheeled toys.

Once invented, wheeled vehicles proved indispensable to civilization, being able to carry goods (i.e., oxcarts), passengers (stage coaches), and soldiers (chariots). In more modern times, we have trucks, automobiles, armored personnel vehicles, and so on.