ORIGIN OF THE OCEANS
K. K. Turekian, Yale University, New Haven, CT, USA
Copyright & 2001 Elsevier Ltd.
Introduction
The oceans and the salts dissolved in them probably all
formed early in the Earth’s history. Although planetary
degassing is occurring, as evidenced by studies of rare
gases in rocks, the oceans, and the atmosphere, there is
also a loss of water to the mantle via subduction.
Supply from and loss to the mantle may be roughly
equal at present.
Acquiring an Ocean
The oceans can be conceived of either as a feature
established in the earliest history of the planet or as
the result of a continuing supply of water and the
constituents of sea water by degassing from the
Earth’s interior.
In 1951 W.W. Rubey, in his Presidential Address to
the Geological Society of America, took the latter point
of view. His arguments were colored by the knowledge
available at that time of the age of the Earth and the
age of the oldest rocks. Based on the analysis of lead
isotopes in galenas, it was determined in the late 1940s
that the Earth was about 3.2 billion years old. Some
continental rocks, presumed to be relicts of ancient
terrains, dated at about the same time also gave ages of
about 3.2 billion years. On this basis it was assumed
that the oldest rocks preserved a record of the dawn of
Earth history. The contemporary oceans and oceanderived sediments contain chemical species in quantities far in excess of those available from the weathering of crustal rocks (Table 1). These components
were called ‘excess volatiles’ by Rubey, but Harold
Urey suggested that they were really better characterized as ‘excess solubles’. If these species all arrived with
an early ocean, the early ocean would have had a
radically different composition. It would dissolve rocks
and also precipitate compounds different from those
depositing from the present ocean.
If that were indeed the case, Rubey argued, the
initial rocks should show the effects of a sudden
supply of ocean water and hydrochloric and sulfuric
acids, and carbon dioxide that ultimately dissolved
rocks and formed the saline sea. The ancient rocks,
however, do not look appreciably different from
younger rocks; thus the absence of a difference in
composition indicates that the oceans with their attendant excess anionic species have grown slowly
with time. Indeed, it was argued that if a small
fraction of the flux of water from fumaroles and hot
springs were primary (from the Earth’s interior) rather than meteoric or surface recycled water, then,
over time, the oceans could be added to the surface
from the interior so that the volume was increasing
with time.
The discovery in 1955 that the Earth as a member
of the solar system was really about 4.55 billion
years old, and that the oldest rocks were considerably younger, ruled out having a record of the earliest
days of the Earth’s existence. In addition, from
measurements of the hydrogen and oxygen isotopes
of hot springs and in some cases tracking radioactive
tritium from nuclear tests in hot springs, it was clear
that all or most of the water in hot springs, and fumaroles was meteoric, and therefore determining a
primary water flux was virtually impossible.
There is evidence, however, that there is planetary
degassing, as revealed in the flux of radiogenic
40 Ar
(Figure 1) and primordial
3
He (Figure 2) to the atmosphere. When these fluxes are used to model the
flux of other gases (or their condensation products),
two results are obtained. Gases that behave like
36 Ar
(the nonradiogenic argon isotope) appear to have
arrived at the Earth’s surface in the earliest days of
Earth history, while carbon dioxide and its condensation products, limestone and organic compounds,
are being recycled via the processes associated with
plate tectonics. One can assume that other chemically reactive analogues like water, behave in the
same way. Like
36 Ar water may have been at the
Earth’s surface early in its history, and like carbon
dioxide it is being recycled.
Table 1 Components of the oceans, atmosphere, and
sedimentary rocks not derivable by weathering of primary
silicate rocks
Chemical species
Amount on Earth’s
surface not derived by
weathering ( Â 10
20 g)
Water
16 600
Total carbon as carbon dioxide
910
Chlorine
300
Nitrogen
42
Sulfur
22
After Rubey (1951).
3
K. K. Turekian, Yale University, New Haven, CT, USA
Copyright & 2001 Elsevier Ltd.
Introduction
The oceans and the salts dissolved in them probably all
formed early in the Earth’s history. Although planetary
degassing is occurring, as evidenced by studies of rare
gases in rocks, the oceans, and the atmosphere, there is
also a loss of water to the mantle via subduction.
Supply from and loss to the mantle may be roughly
equal at present.
Acquiring an Ocean
The oceans can be conceived of either as a feature
established in the earliest history of the planet or as
the result of a continuing supply of water and the
constituents of sea water by degassing from the
Earth’s interior.
In 1951 W.W. Rubey, in his Presidential Address to
the Geological Society of America, took the latter point
of view. His arguments were colored by the knowledge
available at that time of the age of the Earth and the
age of the oldest rocks. Based on the analysis of lead
isotopes in galenas, it was determined in the late 1940s
that the Earth was about 3.2 billion years old. Some
continental rocks, presumed to be relicts of ancient
terrains, dated at about the same time also gave ages of
about 3.2 billion years. On this basis it was assumed
that the oldest rocks preserved a record of the dawn of
Earth history. The contemporary oceans and oceanderived sediments contain chemical species in quantities far in excess of those available from the weathering of crustal rocks (Table 1). These components
were called ‘excess volatiles’ by Rubey, but Harold
Urey suggested that they were really better characterized as ‘excess solubles’. If these species all arrived with
an early ocean, the early ocean would have had a
radically different composition. It would dissolve rocks
and also precipitate compounds different from those
depositing from the present ocean.
If that were indeed the case, Rubey argued, the
initial rocks should show the effects of a sudden
supply of ocean water and hydrochloric and sulfuric
acids, and carbon dioxide that ultimately dissolved
rocks and formed the saline sea. The ancient rocks,
however, do not look appreciably different from
younger rocks; thus the absence of a difference in
composition indicates that the oceans with their attendant excess anionic species have grown slowly
with time. Indeed, it was argued that if a small
fraction of the flux of water from fumaroles and hot
springs were primary (from the Earth’s interior) rather than meteoric or surface recycled water, then,
over time, the oceans could be added to the surface
from the interior so that the volume was increasing
with time.
The discovery in 1955 that the Earth as a member
of the solar system was really about 4.55 billion
years old, and that the oldest rocks were considerably younger, ruled out having a record of the earliest
days of the Earth’s existence. In addition, from
measurements of the hydrogen and oxygen isotopes
of hot springs and in some cases tracking radioactive
tritium from nuclear tests in hot springs, it was clear
that all or most of the water in hot springs, and fumaroles was meteoric, and therefore determining a
primary water flux was virtually impossible.
There is evidence, however, that there is planetary
degassing, as revealed in the flux of radiogenic
40 Ar
(Figure 1) and primordial
3
He (Figure 2) to the atmosphere. When these fluxes are used to model the
flux of other gases (or their condensation products),
two results are obtained. Gases that behave like
36 Ar
(the nonradiogenic argon isotope) appear to have
arrived at the Earth’s surface in the earliest days of
Earth history, while carbon dioxide and its condensation products, limestone and organic compounds,
are being recycled via the processes associated with
plate tectonics. One can assume that other chemically reactive analogues like water, behave in the
same way. Like
36 Ar water may have been at the
Earth’s surface early in its history, and like carbon
dioxide it is being recycled.
Table 1 Components of the oceans, atmosphere, and
sedimentary rocks not derivable by weathering of primary
silicate rocks
Chemical species
Amount on Earth’s
surface not derived by
weathering ( Â 10
20 g)
Water
16 600
Total carbon as carbon dioxide
910
Chlorine
300
Nitrogen
42
Sulfur
22
After Rubey (1951).
3