Geoscience Reference
In-Depth Information
be seen later, laid the platform, built up and largely concluded the next
method of absolute geochronological dating. The fickle scientific
community had eyes only for the new theories based around radio-
activity. Paradoxically, as we shall see, Joly also carried out much
useful research in this developing area, but he himself could never
consign his sodiummethod to the waste basket. Just three years before
he died, Joly accepted some major modifications suggested by the
American Alfred Church Lane (1863-1948) in 1929 which pointed at
a figure of 300million years for the method, but he was not prepared to
concede to the longer timescales then in vogue. In the light of the
well-advanced objections to his 'sodium method' and the findings
from other methodologies, it is somewhat surprising that Joly did
not accept that it yielded erroneously low age estimates. He
obstinately held to his view, and did not acknowledge the more plau-
sible and worthy conclusion of this work, that it probably measured
the age of the oceans.
Joly's method assumed that the oceans formed at the same time
as, or soon after, the formation of the Earth, so as to make little
difference to his age determination. Given the nature of the primordial
and early Earth this cannot have been true, and we now know that
condensation of the oceanic waters from emitted gases took many
millions of years, and that they are older than even Joly's method
might suggest. What Joly's method actually equates closely to is the
residence time of sodium in the oceans. It is now recognised that
sodium spends anything between 70 and 100 million years swilling
around in seawater before it becomes locked again in sediments which
may in turn become lithified into rock. These may eventually be
subjected to uplift and erosion, which would release the sodium
once again into the oceans.
It is interesting to note that, on the basis of research published in
1998 by Paul Knauth in Nature on the volume of chloride contained
in brines found in deep-seated groundwater, it is now thought that the
earliest ocean was 1.5 to 2 times saltier than that of today. The sodium
chloride was formed from the combination of chloride ions derived
