Calibrating Rates of Early Cambrian Evolution

TLDR

The Cambrian began with an explosive diversification, but quantifying its evolutionary rates has been hampered by insufficient high‑precision ages. The study uses uranium‑lead zircon geochronology to date Cambrian rocks. Uranium‑lead zircon dating places the start of the Cambrian at ~544 Ma, shows the Manykaian stage lasted at least 10 Ma, while the Tommotian and Atdabanian stages together spanned only 5–10 Ma, compressing Early Cambrian time and highlighting the rapidity of faunal diversification and turnover.

Abstract

An explosive episode of biological diversification occurred near the beginning of the Cambrian period. Evolutionary rates in the Cambrian have been difficult to quantify accurately because of a lack of high-precision ages. Currently, uranium-lead zircon geochronology is the most powerful method for dating rocks of Cambrian age. Uranium-lead zircon data from lower Cambrian rocks located in northeast Siberia indicate that the Cambrian period began at approximately 544 million years ago and that its oldest (Manykaian) stage lasted no less than 10 million years. Other data indicate that the Tommotian and Atdabanian stages together lasted only 5 to 10 million years. The resulting compression of Early Cambrian time accentuates the rapidity of both the faunal diversification and subsequent Cambrian turnover.