![]() Oxygen only began to persist in the atmosphere in small quantities about 50 million years before the start of the Great Oxygenation Event. This rusting led to the deposition of iron oxide on the ocean floor, forming banded iron formations. The oxygen they produced would have been rapidly removed from the oceans by weathering of reducing minerals, most notably iron. ![]() ![]() Photosynthetic prokaryotic organisms that produced O 2 as a waste product lived long before the first build-up of free oxygen in the atmosphere, perhaps as early as 3.5 billion years ago. Most significantly, the rise of oxygen caused a mass extinction of anaerobic microbes and paved the way for multicellular life.īefore the Great Oxidation Event The increase in oxygen concentrations had wide ranging and significant impacts on life. In the absence of plants, the rate of oxygen production by photosynthesis was slower in the Precambrian, and the concentrations of O 2 attained were less than 10% of today's and probably fluctuated greatly. At current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years. Oxygen began building up in the atmosphere at approximately 1.85 Ga. Small quantities of oxygen were released by geological and biological processes, but did not build up in the atmosphere due to reactions with reducing minerals. īefore photosynthesis evolved, Earth's atmosphere had no free oxygen (O 2). Stages 4 and 5 (0.85 Ga–present): O 2 sinks filled, the gas accumulates. Stage 3 (1.85–0.85 Ga): O 2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer. Stage 2 (2.45–1.85 Ga): O 2 produced, but absorbed in oceans and seabed rock. Stage 1 (3.85–2.45 Ga): Practically no O 2 in the atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago ( Ga). Timeline of the development of free oxygen in the Earth's seas and atmosphere O 2 build-up in the Earth's atmosphere.
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