The standard state of a substance does not have to exist in nature: for example, it is possible to calculate values for steam at 298.15 K and 10 5 Pa, although steam does not exist (as a gas) under these conditions.
A Mesopotamian wheel. Photo source. One of the reasons why the wheel was invented only at this point in history is due to the fact that metal tools were needed to chisel fine-fitted holes and axles. This leads to the next reason â the wheel was not just a cylinder rolling on its edge. It was a cylinder that was connected to a stable, stationary platform.
True (freely-spinning) potter's wheels were apparently in use in Mesopotamia by 3500 BCE and possibly as early as 4000 BCE, and the oldest surviving example, which was found in Ur (modern day Iraq), dates to approximately 3100 BCE.