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________________________________________________________________________
Institute for Creation Research, PO Box 2667, El Cajon, CA 92021
Voice: (619) 448-0900 FAX: (619) 448-3469
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________________________________________________________________________
No. 109 "Vital Articles on Science/Creation" July 1982
________________________________________________________________________
Did the Early Earth Have A Reducing Atmosphere?
by Steven A. Austin, Ph.D.
Copyright (c) 1982 by I.C.R.
All Rights Reserved
________________________________________________________________________
After reviewing evolutionists' speculations on the origin of life,
Clemmey and Badham say, "...the dogma has arisen that Earth's early
atmosphere was anoxic,..."[1] By "anoxic" they mean an atmosphere
without free oxygen gas (O{2}), very different from the oxidizing
mixture we breathe. The generally accepted model for the evolution of
the atmosphere[2] supposes that before about 1.9 billion years ago the
earth's atmosphere was a reducing mixture of nitrogen (N{2}), methane
(CH{4}), water vapor (H{2}0), and possibly ammonia (NH{3}). Solar
radiation and lightning discharges into the reducing gas mixture are
believed by the consensus of evolutionists to have produced natural
organic compounds and eventually life itself. The reason evolutionists
postulate an anoxic and reducing atmosphere is mentioned by Miller and
Orgel, "We believe that there must have been a period when the earth's
atmosphere was reducing, because the synthesis of compounds of
biological interest takes place only under reducing conditions."[3]
If the dogma of the Precambrian reducing atmosphere is true, we would
expect to find geologic evidence in the Archean and lower Proterozoic
strata (believed by evolutionists to be older than 1.9 billion years).
Although altered by diagenesis and metamorphism, the oldest sedimentary
rocks should possess distinctive chemical composition and unusual
mineral assemblages.
PLACERS OF UNSTABLE METALLIC MINERALS
Pebble and sand placer deposits of upper Archean and lower
Proterozoic age occur in southern Canada, South Africa, southern India
and Brazil. Some of these are known to be cemented by a matrix
containing mineral grains of pyrite (FeS{2}) and uraninite (UO{2}).
Pyrite has the reduced state of iron (without oxygen, but with sulfur)
which is unstable as sedimentary grains in the presence of oxygen.
Uraninite has the partly oxidized state of uranium which is oxidized to
UO{3} in the presence of the modern atmosphere. These unstable mineral
grains in gravel and sand concentrates have been claimed by some
geologists to indicate a reducing atmosphere at the time of deposition.
Although ancient placers of unstable metallic minerals occur in
various places, these are by no means the only types of heavy mineral
concentrates known from Archean and lower Proterozoic strata.
Davidson[4] studied heavy mineral concentrates of completely modern
aspect in strata nearly contemporaneous with the unstable concentrates.
If deposition occurred under a reducing atmosphere all sediments would
be expected to contain pyrite. The normally oxidized concentrates could
be better used to argue for oxidizing atmosphere with the unstable
assemblages being accumulated under locally reducing conditions.
Clemmey and Badham[5] are bold enough to propose that the unstable
minerals were disaggregated by mechanical weathering, with limited
chemical and biological weathering, under an oxidizing atmosphere.
Support comes from Zeschke[6] who has shown that uraninite is
transported by the oxidizing water of the modern Indus River in
Pakistan. Grandstaff[7] has shown that the ancient uraninite placers
contain the form of thorium-rich uraninite which is most stable under
modern oxidizing conditions. Pyrite has also been reported in modern
alluvial sediments, especially in cold climates.[8] It is noteworthy that
magnetite, an oxide of iron unstable in modern atmospheric conditions,
is the most common mineral constituent of the black sand concentrates on
modern beaches. Evidently, brief exposures to special oxidizing
conditions are not sufficient to oxidize many unstable minerals. Thus,
these metallic mineral placers do not require a reducing atmosphere.
IRON DEPOSITS
Another frequently cited evidence for an early reducing atmosphere
comes from ancient iron ore deposits called "banded iron formations."
These are common in Archean and Proterozoic strata, the best known being
the ores of the Lake Superior region. The iron deposits consist
typically of thin laminae of finely crystalline silica alternating with
thin laminae of iron minerals. Magnetite (Fe{3}O{4}), an incompletely
oxidized iron mineral, and hematite (Fe{2}O{3}), a completely oxidized
iron mineral, are common in the banded iron formations. Magnetite may
be considered a mixture of equal parts of FeO (iron in the less
oxidized, ferrous state) and Fe{2}O{3} (iron in the oxidized, ferric
state). Because magnetite would be more stable in an atmosphere with
lower oxygen pressure, some evolutionists have argued that banded iron
accumulated during the transition from a reducing to a fully oxidizing
atmosphere some 1.9 billion years ago. Soluble ferrous iron abundant in
the early reducing sea, they suppose, was precipitated as oxygen
produced the insoluble, ferric iron of the modern oxidizing sea.
Three problems confront the transition hypothesis. First, the banded
iron is not _direct_ evidence of a reducing atmosphere, it only
_suggests_ that an earlier reducing atmosphere _may_ have existed.
Other options are certainly possible. The iron formations contain
_oxidized_ iron and would require an _oxidizing_ atmosphere or other
abundant source of oxygen!
A second problem is that the iron formations do not record a
simultaneous, worldwide precipitation event, but are known to occur in
older strata when the atmosphere was supposed to be reducing and in
younger strata when the atmosphere was undoubtedly oxidizing. Dimroth
and Kimberley[9] compare Archean iron formations (believed to have been
deposited at the same time as unstable metallic mineral placers more
than 2.3 billion years ago) with Paleozoic iron formations (believed to
have been deposited in an oxidizing atmosphere less than 0.6 billion
years ago). The similarities can be used to argue that the Archean
atmosphere was oxidizing.
A third problem is that red, sandy, sedimentary rocks called "red
beds" are found in association with banded iron formations. The red
color in the rock is imparted by the fully oxidized iron mineral
hematite, and the rocks are characteristically deficient in unoxidized
or partly oxidized iron minerals (e.g., pyrite and magnetite). Red beds
are known to occur _below_ one of the world's largest Proterozoic iron
formations and have been reported in Archean and lower Proterozoic
rocks.[10] By their association with iron formations, red beds also
indicate oxidizing conditions.
SULFATE DEPOSITS
When sulfur combines with metals under reducing conditions the result
is sulfide minerals such as pyrite (FeS{2}), galena (PbS), and
sphalerite (ZnS). When sulfur combines with metals under oxidizing
conditions the result is sulfate minerals such as barite (BaSO{4}),
celestite (SrSO{4}), anhydrite (CaSO{4}), and gypsum (CaSO{4}*2H{2}O).
If the earth had a reducing atmosphere, we might expect extensive
stratified, sulfide precipitates in Archean sedimentary rocks. These
would not have formed by volcanic-exhalative processes (as some sulfide
minerals do even today), but directly from sea water (impossible in our
modern oxidizing ocean). No deposits of this type have been found.
Instead, Archean bedded _sulfate_ has been reported from western
Australia, South Africa, and southern India.[11] Barite appears to have
replaced gypsum which was the original mineral deposited as a chemical
precipitate. This provides evidence of ancient oxidizing surface
conditions and oxidizing ground water. The extent of the oxidizing
sulfate environment and its relation to ancient atmospheric composition
are speculation, but, again we see evidence of Archean oxygen.
OXIDIZED WEATHERING CRUSTS
When a rock fragment is deposited, its surface is in contact with the
external environment and can be altered chemically. Thus, pebbles and
lava flows in the modern atmosphere weather to form oxide minerals at
their surfaces. Even in the ocean this weathering occurs. In a similar
fashion, Dimroth and Kimberley[12] report oxidative weathering of
pebbles occurring below a banded iron formation and describe hematite
weathering crusts on Archean pillow basalt (believed to represent a
submarine lava flow). Again, Archean oxygen is indicated.
CONCLUSION
Much more could be written concerning the ancient atmosphere.
Water-concentrated, unstable metallic minerals are not diagnostic of
reducing conditions. The many mineral forms of ferrous and ferric iron
in Archean and lower Proterozoic rocks are most suggestive of
oxygen-rich conditions. Sulfate in the oldest rocks indicates oxygen in
the water. Weathered crusts on ancient rocks appear to require oxygen
in both air and water. To the question, "Did the early earth have a
reducing atmosphere?", we can say that reducing evidence has not been
documented in the rocks. An evolutionist can maintain that a reducing
atmosphere existed _before_ any rocks available for study formed, but
such a belief is simply a matter of faith. The statement of Walker is
true, "The strongest evidence is provided by conditions for the origin
of life. A reducing atmosphere is required."[13] The proof of
evolution rests squarely on the assumption of evolution!
REFERENCES
1. Clemmey, H., and Badham, N. "Oxygen in the Precambrian Atmosphere:
An Evaluation of the Geological Evidence." _Geology_, v. 10,
1982, p. 141.
2. Ibid., p. 142.
3. Miller, S.L., and Orgel, L.E. _The Origins of Life on the Earth_.
Englewood Cliffs : Prentice Hall, 1974, p. 33.
4. Davidson, C.F. "The Precambrian Atmosphere." _Nature_, v. 197,
1963, p. 893.
5. Loc. cit., p. 142.
6. Zeschke, G. "Transportation of Uraninite in the Indus River,
Pakistan." _Trans. Geol. Soc. South Africa_, v. 63, p. 87.
7. Grandstaff, D.E. "A Kenetic Study of the Dissolution of
Uraninite." _Economic Geology_, v. 71, 1976, pp. 1493-1506.
8. Clemmey and Badham. loc. cit., p. 142.
9. Dimroth, E., and Kimberley, M.M. "Precambrian Atmospheric Oxygen:
Evidence in the Sedimentary Distributions of Carbon, Sulfur,
Uranium and Iron." _Canadian Journal Earth Science_, v. 13,
1976, pp. 1161-1185.
10. Clemmey and Badham. loc. cit., p. 143.
11. Lambert, I.B., Donnelly, T.H., Dunlop, J.S.R., and Groves, D.I.
"Stable Isotope Compositions of Early Archaean Sulphate Deposits
of Probable Evaporitic and Volcanogenic Origins." _Nature_, v.
276, 1978, p. 808.
12. Loc. cit. p. 1176.
13. Walker, J.C.G. _Evolution of the Atmosphere_. New York, Macmillan,
1977, p. 224.
________________________________________________________________________
Description of change(s):
1. Subscript notation is indicated by: {}.
________________________________________________________________________
________________________________________________________________________
This _Impact_ was converted to ASCII, for BBS use,
from the original article, by GenNet.
Don Barber, ICR Systems Administrator
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in the form of two documents:
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and "Tenets of Biblical Creationism."
(see Impact No. 85)
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