Geoscience Reference
In-Depth Information
The continents do not plow through oceanic crust impelled by unknown forces, rather they ride
passively on mantle material as it comes to the surface at the crest of the ridge and then moves
laterally away from it. . . .
The whole ocean is virtually swept clean (replaced by new mantle material) every 300 to
400 million years. 12
Journeyman Geologist
In 1961, after Hess circulated his preprint but before the 1962 publication of the
Buddington volume, a self-described “journeyman geologist” named Robert Sin-
clair Dietz authored a paper in Nature in which he used the phrase “spreading
seafloor” for the first time. He described the concept, soon to be called seafloor
spreading, at least as fully as Hess. But Dietz was not on Hess's mailing list and in
all likelihood never saw the preprint.
Ordinarily, priority in science is not awarded on the basis of a preprint, which
has not passed peer review and has no particular status. Yet on the basis of his
preprint and because Dietz under pressure ceded precedence, Hess has come to be
accorded priority for seafloor spreading, a key step on the road to plate tectonics.
Dietz, an iconoclast and outsider who never received a government research
grant, espoused not only seafloor spreading but also continental drift and meteorite
impactontheEarthandtheMoon.Heconfrontedorthodoxgeologistswithbizarre,
nonuniformitarian claims, such as that meteorite impact had created the giant Sud-
bury ore body in Canada, the vast and ancient Vredefort Ring in South Africa, and
many other terrestrial craters. Robert Dietz was sometimes wrong, but about two
of the great discoveries chronicled in this topic, he was right. But was he the first
to be right about seafloor spreading, or was Hess?
In his 1961 article in Nature , Dietz wrote that “large-scale thermal convection
cellsoperateinthemantle,”providing“theprimarydiastrophicforcesaffectingthe
lithosphere.” 13 The “sea floor marks the tops of the convection cells and slowly
spreads from zones of divergence to those of convergence.” 14 Blocks of continent-
al crust are “rafted to down-welling sites and then . . . stabilized in a balanced field
of opposing forces.” Continents do not “sail through the sima,” regarded by many
as a nearly insurmountable flaw in Wegener's model; they either “move along with
it or stand still” over a down-welling site (856).
As to the then-inexplicable magnetic-anomaly stripes of Raff and Mason, Dietz
said they show “a striking north-south lineation which seems to reveal a stress pat-
tern. Such interpretation would fit into spreading concept [ sic ] with the lineations
being developed normal to the direction of convection creep. Great mobility of the
sea floor is thus suggested” (857). 15 Reading Dietz's words with decades of hind-
Search WWH ::




Custom Search