The Precambrian Era began with the origin of the Earth about 4.6 billion years ago and ended 543 million years ago. Life on Earth was uncommon until late in the Precambrian and consisted mainly of bacteria and protists. This piece of Precambrian Banded Iron Formation collected in northern Wisconsin is over 2 billion years old and provides evidence of bacterial life during the Precambrian and also of the composition of Earth's early atmosphere.