Mesoproterozoic

The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today, although their arrangement on the Earth's surface was different.

The Stenian Period ( , from , meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically due to the scarcity of Precambrian fossils and lack of reliable zonation. It is preceded by the Ectasian Period and followed by the Neoproterozoic era and the Tonian period.

The Ectasian Period (from , meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The Calymmian (from , meaning 'cover') is the first geologic period in the Mesoproterozoic Era, lasting from to million years ago (Ma) and spanning 200 million years. It follows the Statherian Period from the Paleoproterozoic Era, and precedes the Ectasian Period. Instead of being based on stratigraphy, these dates are defined chronometrically.

hornblende-biotite granite containing large round crystals of orthoclase each with a rim of oligoclase

Bangiomorpha pubescens is a species of red algae in the order Bangiales. It is the first known sexually reproducing organism. A multicellular fossil of Bangiomorpha pubescens was recovered from the Hunting Formation in Somerset Island, Canada that strongly resembles the modern red alga Bangia despite occurring in rocks dating to , during the Stenian period. This species is the oldest example of an organism belonging to an extant phylum. The fossil includes differentiated reproductive cells that are the oldest evidence of sexual reproduction. Sexual reproduction increased genetic variation, whi