although in certain areas the advent of a new metallic technology seems to
have taken place earlier.
     Whatever the chronological and regional differences in these cultures,
together they provided the preconditions of the future Iron Age.
                        INVENTION OF WHEEL
  The wheel is probably the most important mechanical invention of all
  time. Nearly every machine built since the beginning of the Industrial
  Revolution involves a single, basic principle embodied in the wheel. It’s
  hard to imagine any mechanized system
  that would be possible without it. From tiny watch gears to automobiles,
  jet engines and computer disk drives, the principle is the same. Based on
  diagrams on ancient clay tablets, its earliest known use was a potter’s
  wheel that was used at Ur in Mesopotamia as early as 3500 BC. The first
  use of the wheel for transportation was probably on Mesopotamian
  chariots in 3200 BC. It is interesting to note that wheels may have had
  manufacturing applications before they were used on vehicles.
  It is easy to assume that the wheel would have simply "happened" in every
  culture when it reached a particular level of sophistication. However, this
  is not the case. The great Inca, Aztec and Maya civilizations reached an
  extremely high level of development, yet they never used the wheel. In
  fact, there is no evidence that the use of the wheel existed among native
  people anywhere in the Western Hemisphere until well after contact with
  Europeans. Even in Europe, the wheel evolved little until the beginning of
  the nineteenth century. However, with the coming of the Industrial
  Revolution the wheel became the central component of technology, and
  came to be used in thousands of ways in countless different mechanisms.
Earliest Agrarian Settlements
None of the Neolithic sites in the Indian subcontinent is older than 7000–
6000 BC, while some found in south India and eastern India are as late as 1000
BC. However, the main period of the Neolithic Age in the Indian subcontinent