Columbia (also known as Nuna and, more recently, Hudsonland or Hudsonia) is the name of one of the Earth's earliest supercontinents, which existed approximately 1.8 to 1.5 billion years (Ga) ago in the Paleoproterozoic Era. It consisted of the proto-cratons that made up the former continents of Laurentia, Baltica, Ukraine, Amazonia, Australia, and possibly Siberia, North China and Kalahari as well. The existence of Columbia is based upon paleomagnetic data .