Ok, so not that 'where on earth', like literally - 'Where on Earth'.
Where on Earth, can you find matter in the 4th state, i.e. the plasma state?
Plasmas are a common part of the world we live in. The definition of plasma allows them to exist within an environment consisting mostly of bound atoms.
A variety of human technology creates plasmas. The type I hear plasma researchers reference most is a simple RF Plasma. This is perhaps the most direct way to use electricity to shake off the electrons from their atoms within a confined volume by using fast oscillating electromagnetic fields.
Nature also creates plasma. An Aurora is certainly included. Many less "exotic" plasma states are much more common. A fire has a low population of the ionized species, but is still a plasma. From the Wikipedia plasma article:
See Wikipedia for a list of available plasmas over there..! Or have a look below for the chart which shows variation of temperature and electron density in different plasmas..!
A quick Googling would've provided the answer. Common examples include