The Mesoarchean (pronunciation: /ˌmiːzoʊ.ɑːrˈkiː.ən/, also spelled Mesoarchaean) is a geologic era within the Archean, spanning 3,200 to 2,800 million years ago. The period is defined chronometrically and is not referenced to a specific level in a rock section on Earth. Fossils from Australia show that stromatolites have lived on Earth since the Mesoarchean. The Pongola glaciation occurred at 2,900 million years ago. The first supercontinent Vaalbara broke up during this time around 2,800 million years ago.