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This paper reviews chemical data pertaining to the materials of the earth’s crust which is considered to consist of the outer envelopes of the earth down to the M discontinuity. Estimates are given for average compositions and total amounts of major elements for the hydrosphere, atmosphere, and biosphere, with total mass respectively 1644, 5.1, and 0.01 × 1015 metric tons. The lithosphere consists of sediments and crystalline rocks with a total mass of 23,000–24,000 × 1015 metric tons. Average compositions are given for the most widely distributed sediments and crystalline rocks of the lithosphere. Two contrasting regions are recognized within the lithosphere: a deep-oceanic region (area 268 million km2, average depth below sea level 4½ kms, thickness 6 kms, mostly basaltic rocks) and a continental shield region (area 105 million km2, average height above sea level ¾ km, thickness 35½ kms, mostly rocks approaching granodiorite in average composition). Two auxiliary regions are recognized which are chemically intermediate between these two main regions of the globe: a region of young folded belts (area 42 million km2) and a sub-oceanic region (continental platforms and slopes, some marginal trenches, area 93 million km2). The remaining 2 million km2 of land are essentially volcanic islands in the deep-oceanic and suboceanic regions. Estimates are given for each of these regions, after which the lithosphere as a whole is considered.

Amounts of major hyperfusible constituents in the earth’s crust are estimated at: H2O 1800–2700, CO2 250, CI 35–40, N 6–8, and S 4–7 × 1015 metric tons. Total chemically bound and free oxygen in the crust is of the order of 10,000–15,000 × 1015 metric tons.

In an appendix a synthesis is attempted of the chemical evolution of the earth’s crust from earliest geologic times, when the primitive planet had an atmosphere of hydrogen, nitrogen, water vapor, methane, and ammonia, a relatively small hydrosphere, and a thin crust of pumiceous silicic materials, to present times as detailed in the major part of the paper. The development of the present chemical composition and distribution of materials in the crust of the earth is thought to have been dominated by changes in the mantle throughout geologic time, notably accretion of the iron core, degassing, and partial melting in the upper parts of the mantle. Within the lithosphere further redistribution and differentiation of materials were effected by a continuous cycle of weathering, transport, sedimentation, and plutonic metamorphism with attendant igneous activity, starting at the chemically active boundary with the atmosphere and aided at lower levels in the crust by heat, fluxes, and felsic constituents derived from the mantle. Pronounced changes in composition of atmosphere and hydrosphere in geologic time can hardly have failed to influence chemical trends of some of these processes.

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