quality:corruption
Continental indicators

Paleosols, detrital grains, and red beds are evidence of low oxygen levels. Paleosols (fossil soils) older than 2.4 billion years old have low iron concentrations that suggest anoxic weathering. Detrital grains composed of pyrite, siderite, and uraninite (redox-sensitive detrital minerals) are found in sediments older than ca. 2.4 Ga. These minerals are only stable under low oxygen conditions, and so their occurrence as detrital minerals in fluvial and deltaic sediments are widely interpreted as evidence of an anoxic atmosphere. In contrast to redox-sensitive detrital minerals are red beds, red-colored sandstones that are coated with hematite. The occurrence of red beds indicates that there was sufficient oxygen to oxidize iron to its ferric state, and these represent a marked contrast to sandstones deposited under anoxic conditions which are often beige, white, grey, or green.