Radicecology
pexe 562
the crust of the earth, in sea water, the
* amounts of elements supplied to sea water
tot rhe percentage of those supplied which are
asa
in
ou”
the composition of the material from which
3 o
earth was formed may be estimated from the
the dapce of the elements in the solar atmosore
In this material hydrogen, helium, and
peer account for 99,7 per cent of the total
oxvk" of the remaining elements only iron is
©=
y“
te
BS
7.
“ae
solution.
resent in relatively high (0.167 per cent) amount
fo gnd contr ibutes
;
97.4 per cent of the total mass of
the transition elements vanadium, manganese, iron,
Had iron not been
nickel, and copper,
roduced in relatively large quantities, due to
egbdalt,
rts high nuclear binding energy,
the subsequent
role of iron in the formation of the earth and its
Pe availability for use by organisms probably would
have been Significantly reduced,
Fractionation of elements occurred in the
: early molten stages of the earth and, the pre-
:
EE
E
F
dominant elements at this time were iron, oxygen,
mignesium, and silicon (Table 1), The amount of
oxygen was not sufficient to convert the cationic
elements into oxides so that a major part of the
tron and nickel in elemental form sank to the
center forming the core, Most of the cobalt,
mulybdenum, and other heavy metals were carried
‘along and a major part of the iron and other heavy
r metals was thereby effectively removed from the
environment which was later to be inhabited by the
| biosphere (Mason, 1958),
A mantle and crust solidified over the core
and the latter was enrtched in sodium, aluminum,
f potassium, Chlorine, calcium, phosphorus, silicon,
fF and oxygen,
Iron contributed only about one-
p seventh and cobalt about one-one hundredth as much
F of the crust as they did of the total earth, and
; in addition, nickel, sulfur, and magnesium were
reduced in amount, Although the percentage of
iron was reduced in the crust of the earth in relation to that in the core,
it was present in ap-
preciable amounts with only oxygen, silica, and
aluminum being more abundant.
With the formation of the hydrosphere many of
the elements of the crust were redistributed. The
mobility and chemical forms of iron and cobalt were
and are influenced by the environmental conditions
on land and in the water and were affected significantly by physical and chemical action of the
atmosphere, The paths of iron and cobalt were
probably from weathered rock,
to fresh water,
to
the seas where a major part of the iron and a
lesser part of the cobalt was precipitated and deposited at the bottom.
In many instances the bottoms of the seas were raised to altitudes higher
than the surface of sea and the cycle was repeated.
Thus, leaching of the earth’s crust was an inm-
Purtant factor in the distribution and deposition
of iron and cobalt in both
hydrosphere,
5a2
the lithosphere and
In natural yater, iron is present as Feo+
©, and Fe(OH)“+,.
Iron, in the ferrous form,
ae rains in solution with precipitation occuring
: ter its oxidation to the ferric state. The
solpoort of ferric hydroxide is dependent upon its
oh ubility which, in turn, is dependent upon the
tb of the medium. At pH six, ferric hydroxide is
ions 100 times as soluble as at pH seven and is
1937.00 times as soluble as at pH 8.5 (Cooper,
).
Iron in weakly acid streams flowing into
‘the
alkalseas therefore is p.ecipitated in the slightly
the
ine
sea water.
This fact is illustrated by
fresh oevations that the average iron content of
na
waters is about 100 times the level found in
rine waters (Mason, 1958).
The precipitation of iron in sea water from
acidic iron wastes was described by Ketchum and
Ford (1952). After the introduction of the wastes,
the sea water first became green from the formation of ferrous hydroxide, Later the oxidation of
the iron to ferric hydroxide resulted in a floculent red precipitate,
In addition to direct observations, an
estimate of the behavior of chemical elements in
the oceans may be made from the geochemical balance
of the elements in sea water,
If the comparison
is made of the total amount of the elements supplied to the seas from the lithosphere with the
amounts now found in sea water, the transfer percentage for each element may be determined. The
larger the transfer percentage for a given ele-
ment, the more of that element has remained in
solution. In Table 1 are given the amounts of
several elements in sea water, the amounts sup-
plied to the sea, and the percentage of each element which is in solution. Iron has the lowest
transfer percentage of any of the elements with
only one part in three million of that criginally
supplied remaining in solution. Manganese exhibits a transfer percentage ten times and the other
transition elements cobalt, nickel and copper 100
to 200 times that of tron, In absolute amounts,
however, iron is present in sea water at a level
about three times that of copper, five times that
of vanadium, manganese and nickel, and twenty
times that of cobalt. However, all of the tran-
sition elements, including iron, are present in
very low amounts,
The role of iron in the respiratory pigments
of animals may be related to the distribution of
this metal in the different environments and to
the levels of available oxygen, The two principal metals contained in respiratory pigments are
iron and copper in that order of occurrence.
The copper containing pigment (hemocyanin), probably originated mostly among plankton and free
swimming forms of ancient invertebrates which
inhabited marine waters containing low amounts of
iron and relatively high oxygen content. The
iron containing pigment (hemoglobin) probably
originated and developed at about the same time
in organisms that lived at the ocean bottom,
especially in those organisms which burrowed in
the bottom sediments, where iron was and is
available in relatively high amounts and oxygen
was at a reduced level (Vinogradov, 1953), In
most of those animals which made the transition
from salt to brackish or fresh water or onto the
land mass, the respiratory pigments contain iron,
The high levels of iron available to terrestrial,
fresh water, and bottom dwelling marine organisms,
in contrast to the reduced amounts available to
free living marine organisms, probably influenced
the incidence of utilization of iron by the inhabitants of the different environments.
Iron, when precipitated in sea water, forms
a positively charged colloid and the precipitate
carries scavenged ions with it as it settles to
the bottom. Many ions, including arsenic, molybdenum, nickel, vanadium, phosphorus, antimony,
copper, selenium, and lead, are removed from
solution by this mechanism, In addition, the
manganous ion may be catalytically oxidized by a
gel of ferric hydroxide hydrate and this reaction
probably accounts in part, at least, for the low
transfer percentage of manganese in comparison to
vanadium, cobalt, nickel, and copper.
The co-
precipitate of manganese and iron is capable of
removing additional ions from the sea water, in-
cluding cobalt, zinc, thorium, tin, and silver
(Arrhenius, 1959),
The removal of heavy ions by ferric hydroxide
is of great importance in the survival of past
nom ARCHUYE®
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