Earth’s sedimentary crust

Dr. F. J. Pettijohn, in Sedimentary Rocks (pp. 360-61), says that complete evaporation of a 1,000-foot column of sea water would leave but 15 feet of salts, of which 0.4 feet would be calcium sulphate, 11.6 feet halite and 3 feet potassium and magnesium-bearing salts. Salt beds thousands of feet thick would therefore require evaporation of a very great volume of sea water, whereas the deposits bear evidence (mud cracks, etc.) of shallow-water origin.

He says that many evaporate deposits do not show the characteristics the theory demands and concludes that simple evaporation of sea water did not occur, and either the present brine was not formed from sea water or the evaporation took place under special conditions that will explain the anomalies.

To assume that all salt in oceans and inland beds was leached out of plutonic, igneous rock, constitutes a denial that Earth was ever hot enough to vaporize sodium chloride and repel it to the primordial atmosphere. The assumption also necessitates the belief that salt was created and remained within the molten mass while the latter was cooling to form Earth’s igneous rock shell. The chemical constitution of all igneous, crystalline, plutonic rocks, as found today, certainly fails to sustain such an assumption.

Rather, does it not seem more probable that sodium and chlorine were combined into salt during some formative, incandescent, flaming stage of Earth’s evolution; that the vaporized product was hurled aloft; that it remained in a revolving primordial atmosphere until Earth’s core had cooled enough so that the salt vapors could condense and descend to Earth? This more logical conception makes it evident that the descending precipitates fell both in the oceans and on the lands. Falling thus on land, probably mixed with or dissolved in water, vast amounts quite naturally could either fall in restricted regional concentrations, just as snow and rain fall regionally today; or could, after falling, be washed to concentrated beds. Falling in the oceans, salinity of the latter would result without involving the assumption that all salt came from igneous rocks of the lands—rocks which, judging by the composition of igneous rocks today, never contained the salt.

Sulphur Deposits

Or, consider the case of elemental sulphur deposits. Sometimes, free sulphur is found in surface outcrops and in pits at shallow depths. However, large deposits of commercial importance are found at depths usually of from a few hundred to 2,000 feet. Many millions of tons of sulphur are required annually to fulfill the world’s needs. In the United States alone some ten million long tons are consumed per year.

Sulphur, in its many allotropic forms, is the fourth most plentiful element on Earth and is widely distributed. In all cases, “free” or elemental sulphur, as distinguished from compounded sulphur, is a sedimentary deposit. In Sicily, the principal source of sulphur prior to 1900, sulphur is found associated with gypsum and bituminous marl and is mined like coal and iron. In and contiguous to the Gulf of Mexico, the principal source of the present world supply, elemental sulphur is found in porous calcite overlying salt domes. It is melted underground by hot water pumped down into the deposits and is forced up to the surface in liquid form by compressed air. It is allowed to flow into huge “vats” where it cools and solidifies. To a considerable extent, however, it is shipped in hot liquid form to consumers. The product is more than 99% pure.

Free sulphur is not a chemical compound—it is a basic, nonmetallic element of complex atomic structure, insoluble in water—an element which must have been fused by the intense heat during Earth’s earliest formative eons. On preceding pages we questioned how all the salt in oceans and on continents could have been accumulated from sediments eroded out of igneous rock. Now we wonder how free-sulphur deposits which overlie salt domes of the Gulf region could have come from a like source. If they did, where were the source rocks situated?

Characteristically, throughout the world, native sulphur is found in sedimentary beds closely associated with gypsum and calcite. How it was deposited and accumulated in such beds is a mystery which geologists admit they have been unable to solve. One theory is that sulphur and gypsum were deposited by action of hydrogen sulphide on calcium carbonate. Another supposition is that sulphur was formed through reduction of sulphate by organic agencies. It is also said that it may have been formed by certain anaerobic bacteria which are able to reduce mineral sulphates.

It would seem to be indubitable that, in the beginning, creation of the element sulphur must have preceded formation of compounds of the element. Hence it would appear illogical to imagine that free sulphur now on Earth was all derived from breakdown of sulphides and sulphates. If all free sulphur on Earth came from weathering of igneous rocks which formerly contained it, igneous rocks still existing throughout the world and available for analysis should corroborate the theory by disclosing considerable percentages of free sulphur as components. But they do not. The sulphur they contain appears invariably in the form either of sulphates or sulphides. Except for small amounts accumulated from solfataras and mineral springs, free sulphur is found in appreciable quantities only in sedimentary rocks.

Strata Variations

But for the sake of argument let it be granted that the original crust of igneous rock did contain all elements and most compounds now found in Earth’s aqueous, sedimentary super-crust. Some strata are siliceous, some calcareous, some alumi-niferous, some carbonaceous, some metalliferous, etc. There are thick unadulterated strata of shales, of sandstones, of limestones, of dolomites, etc., covering extensive regional areas. Whether they were separated or indiscriminately mixed in the source rocks, how could such different chemical compounds be separately dissolved, or weathered and eroded, transported, without adulteration, over considerable distances and deposited each by itself in distinct, separate beds and accumulations? Certainly, detritus, which is being transported and deposited anywhere today, shows no sign whatsoever of any such sorting and differentiation. Invariably, the mixture, like the fellow in the song, is “all shook up.” The farther sediments were transported and the more times they were “reworked,” the less would they have remained distinct and separate from each other.

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