if they are dealing with a paleosol. Some of these structures are very helpful when narrowing down the paleosol that is being identified. However, any paleosol should be verified geochemically before use in proxy-based reconstructions; post-deposition alteration processes, such as potassium metasomatism, can change a paleosol's chemistry without dramatically altering its physical appearance. Applications Paleoclimate reconstructions Because rates and styles of weathering are dependent on climatic factors, paleosols can be used to reconstruct variables of past climate. Mean annual precipitation (MAP) and air temperature (MAAT) are two commonly-reconstructed variables which, along with seasonality and in conjunction with other paleoenvironmental tools, can be used to describe past terrestrial climates. A suite of paleoclimatic proxies exist and while they vary in focus, many rely on changes in chemical composition throughout a soil profile that occur during weathering, burial, and post-burial processes. Their use depends on factors such as post-burial alteration, parent material, and soil order; not every proxy is applicable to every paleosol. Most proxies are applicable to Phanerozoic paleosols (not older), as landscape processes changed dramatically after the rise of land plants. Seasonality (the presence and strength of seasons) requires a more nuanced reconstruction approach. Proposed seasonality proxies primarily rely on a soil wetting/drying process, during which pedogenic carbonate can form; like other proxies, this tool is continually being tested and refined. Paleoatmosphere reconstructions Soils form in near-constant contact with the atmosphere, so their chemical composition is affected by the composition of the atmosphere through both direct and indirect pathways. The oxidation of paleosols has been used as an indicator of atmospheric oxygen, which has risen over Earth's history. Paleosols have also been used to reconstruct atmospheric carbon dioxide levels, based on modern studies of soil carbon gas exchange, carbon isotopes in pedogenic carbonate nodules, and mass-balance approaches taking multiple atmospheric gases (typically carbon dioxide, oxygen, and methane) into account. These methods are being actively developed in the field of early Earth research. Paleobotany Paleosols are an important archive of information about ancient ecosystems and various components of fossil soils can be used to study past plant life. Paleosols often contain ancient plant materials such as pollen grains and phytoliths, a biomineralized form of silica produced by many plants such as grasses. Both pollen and phytolith fossils from different plant species have characteristic shapes that can be traced back to their parent plants. Over long geological time scales, phytoliths may not