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How did silicate-rock weathering remove carbon dioxide from the Ordovician atmosphere?

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Ordovician paleogeography — Ordovician Period The distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Ordovician Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

Silicate-rock weathering removes carbon dioxide from the atmosphere through a chemical process involving precipitation and groundwater. Atmospheric carbon dioxide dissolves in water to form carbonic acid, a weak acid that reacts with silicate rocks exposed at the Earth's surface.1

This weathering reaction converts the solid minerals into soluble products, including bicarbonate ions ( $H C O_{3}^{-}$ ) derived from the original carbon dioxide. These bicarbonate ions are eventually transported to the ocean, where they can combine with calcium ions to form solid calcite ( $C a C O_{3}$ ), the primary mineral in limestone. Once this material is incorporated into seafloor sediments, the carbon is effectively sequestered from the atmosphere.1

During the Ordovician Period, this removal mechanism was influenced by tectonic activity. Increased orogeny and mountain-building uplift during the later Ordovician accelerated the weathering of silicate rocks, which helped draw down atmospheric carbon dioxide levels. Conversely, periods of extensive continental flooding and the lack of widespread land vegetation earlier in the period suppressed these weathering rates, contributing to higher atmospheric carbon dioxide concentrations.2