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Chemical weathering takes place when water, oxygen, carbon dioxide, and other chemical substances react with rock to change its composition. These reactions convert some of the original primary minerals in the rock to secondary minerals, remove other substances as solutes, and leave the most stable minerals as a chemically unchanged resistate .
The submergence of Laurentia ended a lengthy period of widespread continental denudation that exhumed and deeply eroded Precambrian rocks and exposed them to extensive physical and chemical weathering at the Earth's surface. As a result, Powell's Great Unconformity is unusual in its geographic extent and its stratigraphic significance. [6] [7]
The archaeologist Philip A. Barker gives the example of a late Roman period (probably 1st-century) tombstone from Wroxeter that could be seen to have been cut down and undergone weathering while it was in use as part of an exterior wall and, possibly as late as the 5th century, reinscribed for reuse as a tombstone. [1]
Lithosequences include soils that have undergone relatively similar weathering conditions, so variations in composition are based on the relative weathering rates of parent minerals. Therefore, the weathering rates of these soils and their compositions are primarily influenced by the relative proportion of minerals in the Goldich dissolution ...
General Sherman appears to be holding up well (not bad for a 2,200-year-old), but because of pests and climate change, the largest tree in the world needs a checkup
Deposits of loess from subsequent glacial periods have in filled volcanic fissures over millennia, [7] resulting in volcanic basalt and loess as the main sediment types available for deposition in Akaroa Harbour Figure 2. Map of Akaroa Harbour showing a fining of sediments with increased bathymetry toward the central axis of the harbour.
The landforms look very much like karst topography that forms in areas underlain by limestones, but since the rocks that form danxia are sandstones and conglomerates, they have been called "pseudo-karst" landforms. They were formed by endogenous forces (including uplift) and exogenous forces (including weathering and erosion). [2]
NASA scientists found Camp Century, an abandoned Cold War military base, during a flight to map the Greenland Ice Sheet.