biostudies-literatureUnknown111(11)Mills DBA rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth's surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850-542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635-542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survivProceedings of the National Academy of Sciences of the United States of America4168-72https://www.ebi.ac.uk/biostudies/studies/S-EPMC3964089biostudies-literatureOxygen requirements of the earliest animals.PMC3964089Forth MCanfield DESweeten BMills DBWard LMJones CTreusch AHfalseOxygen requirements of the earliest animals.A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth's surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850-542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although multiple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635-542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can surviv2014-01-01T00:00:00Z2014 Mar2026-05-07T06:24:36.878Z2026-04-07T22:40:07.778ZS-EPMC39640892455046710.1073/pnas.1400547111