128 | Great Geologists
Dan McKenzie
Plate tectonics is the defining geoscience
paradigm of the second half of the 20 th
century. 2017 was designated its 50 th
anniversary by The Geological Society
of London because, in 1967, a paper
was published that is widely regarded
as marking the completion of the initial
development of the plate tectonic
thesis. This paper, The North Pacific: An
Example of Tectonics on a Sphere, by
Dan McKenzie and Bob Parker, provided
the model to describe the translations
and rotations on a sphere that, thereby,
define plate motions. McKenzie has
brought much more to geoscience than
just this brilliant paper. He is one of the
pre-eminent geophysicists of the late
20 th to early 21 st century and has made a
telling contribution to our understanding
of processes operating both within the
mantle and the crust.
McKenzie was born in Cheltenham
in 1942. His father was a doctor on
Harley Street in London, and his mother
was noted for her work in garden
design and as an author. He attended
Westminster School, and after winning
a state scholarship in pure and applied
mathematics, McKenzie entered King’s
College, Cambridge in 1960 to study
the natural sciences. Mathematics
was not considered as being one of
the three core scientific subjects in the
Natural Science Tripos, so alongside
physics and chemistry, McKenzie chose
geology after chancing upon Charles
Lyell’s ‘Principles of Geology’ and
Archibald Geikie’s ‘Ancient Volcanoes
of Great Britain’ in the school library.
Unfortunately, geology was to prove
an initial disappointment for McKenzie.
He found the lectures dull (especially
those that focused on palaeontological
classification and zonation), so he
dropped the subject at the end of his
first year.
Following his graduation, he stayed on
at Cambridge as a graduate student
working with Edward (“Teddy”) Bullard,
the pioneering marine geophysicist.
McKenzie became interested in how
the interior of the earth convects,
something completely speculative
at that time. He taught himself fluid
mechanics and then went to the
Scripps Institution of Oceanography at
the University of California, San Diego
as a visiting scholar. This visit ended
hastily after eight months. He had
mistakenly travelled on an immigration
visa, making him liable for the draft to
fight in the Vietnam War. So McKenzie
returned to Cambridge, submitting his
PhD thesis in 1966, but not before he
attended a scientific meeting in New
York that was to provide an impetus for
his research into plate tectonics.
After he heard lectures by Fred Vine
on sea floor spreading and magnetic
anomalies, McKenzie applied his
knowledge of thermodynamics to the
problem of how plates move and came
up with a model that demonstrated a
far more dynamic Earth than anyone
Dan McKenzie in the Geological Society
Library in 2017. Photograph reproduced with
permission of The Geological Society.
had previously thought. He suggested
there are two layers in the mantle, each
of which is in motion, controlling the
movement and behaviour of the tectonic
plates above. He published a key paper,
The Viscosity of the Lower Mantle, in
1966.
Prior to 1967, plate tectonics had a long
gestation period, beginning with Alfred
Wegener’s continental drift (if not the
ideas of others before him), and required
a whole series of observations during the
late 1950s and early ‘60s, including data
on the bathymetry of the deep ocean
floors and the nature of the oceanic
crust. More generally, the development
of marine geology gave evidence for the
association of seafloor spreading with
mid-oceanic ridges and magnetic field
reversals, as published between 1959 and
1963 by Heezen & Tharp, Dietz, Hess,