paleosol

Paleosols also provide valuable clues, as they were in equilibrium with the prevailing atmosphere. From analyses of early Precambrian paleosols it has been determined that the oxygen content of the atmosphere 2.2 billion years ago was one hundredth of the present atmospheric level (PAL).

…many colourful buried soils or paleosols that formed during periods which were both warmer and wetter than today. Thus, on stable tablelands with minimal erosion, the succession provides an exceptional climatic and chronological record that extends back 2.4 million years to the late Pliocene. In total, up to 44 climatic…

…greater depth are known as paleosols. Some features of these soils can serve as climatic indicators, the most reliable being robust features such as horizons with hardened accumulations of relatively insoluble iron, manganese, or calcium minerals or layers with accumulations of strongly aggregated clay-size particles. Given a knowledge of the…