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Earth and Space Sciences · 术语表

什么是 Snowball Earth; cap carbonate？

又称： snowball Earth · cap carbonate

Definition 18.14 University Earth and Space Sciences — Year 2 · 第 18 章 — The Precambrian Earth

A snowball Earth is a state of the Earth in which ice covers the oceans and the continents down to the equator, with grounded ice sheets reaching the sea at all latitudes, for millions of years. A cap carbonate is the layer of carbonate rock, typically a pale, finely laminated dolostone, that sharply overlies the glacial deposits of a snowball and records its sudden end.

A cap carbonate: laminated dolostone of the Nuccaleena Formation, Flinders Ranges, South Australia, resting on the deposits of the Marinoan glaciation (the beds are tilted). Photograph James St. John, CC BY 2.0 (Wikimedia Commons).

示例

Example 18.16 (How long to escape?)

The highest preferred estimate of today’s volcanic release is $0.26\,\mathrm{Gt}$ of carbon dioxide a year. Estimates of the mixing ratio needed to end a Cryogenian snowball range from 0.01 to 0.1. With $M_{\text{a}} = 5.1 \times 10^{18}\,\mathrm{kg}$ , $\bar M = 28.97\,\mathrm{g}\,\mathrm{mol}^{-1}$ and $M_{\mathrm{CO_2}} = 44.01\,\mathrm{g}\,\mathrm{mol}^{-1}$ , $x = 0.01$ takes $\frac{0.01}{0.99}\times1.519\times5.1 \times 10^{18}\,\mathrm{kg} / 0.26 \times 10^{12}\,\mathrm{kg}\,\mathrm{yr}^{-1} = 0.30\,\mathrm{Myr}$ , and $x = 0.1$ takes $3.3\,\mathrm{Myr}$ .

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