Times , 18th September 2003
BITTER ARGUMENT IS DIVIDING GEOLOGISTS
MOST MODERN scientific disputes are
conducted almost clandestinely, their scandal-making
potential confined to the pages of academic journals.
These are where scholars line up to swear their allegiances,
politely sitting on one side of a fence while acknowledging
the right of their opponents to sit on the other, and
willing to swap sides in the face of fresh evidence.
Not so for the geological community,
which has been riven for months by acrimonious arguments
over the existence of “mantle plumes”, fountains
of rock that supposedly spew periodically from inside
The eruptions punch through the land above, creating
huge humps in the landscape. Plate tectonics, which
describes the features of the Earth’s crust in
terms of several interlocking plates that move relative
to each other, struggles to explain why volcanic islands
such as Hawaii should appear in the middle of plates
as well as at the turbulent edges, where plates crash
into and slide beneath each other.
Hot, unpredictable plumes from the
deep interior provided the perfect solution, and have
become a plank of modern geological theory.
Now, bolstered by the fact that experiments
have not yet proved their existence, a small but vocal
group of geologists is raising the heretical possibility
that mantle plumes do not exist at all. Led by Dr Don
Anderson, from the California Institute of Technology,
and Dr Gillian Foulger, from Durham University, the
self-styled aplumatics are pitting themselves as Davids
against the “assume-a-plume” Goliaths.
Plate tectonics, they argue, can also
explain anomalous, mid-plate island chains such as Hawaii.
There is no need to complicate matters, they say, with
the addition of hot plumes rising mysteriously from
nearly 3,000km (1,864 miles) down in the bowels of the
planet. There is, they protest, no evidence of narrow
columns piercing the whole mantle and emerging at the
Earth’s surface, and, moreover, that unbelievably
high pressures in the mantle stop rock from rising,
let alone in the suggested plumes. But they cast their
net of criticism considerably wider — they accuse
the plumatic lobby of discarding or ignoring evidence
that does not fit with their cause, and complain that
Earth-sciences journals are run by editorial boards
with a vested interest in keeping plumes alive.
WERE TAKEN ABACK AT THE VEHEMENCE AND VIULENCE OF THE
As unfavourable pieces of evidence
trickle in, Foulger fumed recently, “plume enthusiasts
have responded to these challenges with creativity.
Carefully truncated cross sections, with colour scales
cranked up, give noisy images the illusion of strong
anomalies traversing the mantle... In 2002 several hundred
papers about them are listed by the Science Citation
Index, so the subject is paying a lot of mortgages.
The assume-a-plume approach has also relieved researchers
of the hard work of thinking up new theories —
a welcome relief in these days when we are all expected
to publish six papers a year or else.”
Anderson even ranks it alongside some
of the most notorious frauds and misconceptions in scientific
history: “(Plume theory) has so many variants,
exceptions, rationalisations, ad hoc adjustments and
failed predictions that it is unsatisfactory at the
most basic level... It is the same kind of wishful thinking
and self-delusion that we associate with Ptolemy, Piltdown,
phlogiston, polywater and cold fusion.”
No wonder then that the forum for these
outpourings, the newsletter of the Geological Society
of London, gives warning that any contributions might
be amended “for possibly legal reasons”.
So outraged was Andy Saunders, professor
of geochemistry at Leicester University, that he felt
compelled to stick up for the plume model, which he
says still convinces most of the geoscience community.
“A number of us were taken aback at the virulence
of these attacks,” Saunders says. “Normally
I wouldn’t get involved but someone had to stand
up to it.”
And so Saunders entered the fray by
penning an article: “Like the electron, which
is never seen, but whose effects are predictable and
observed, plumes are elusive, hidden, enigmatic, and
important... Many aspects of both plate tectonic and
plume models remain imperfectly understood, yet because
something doesn’t fit our prejudice, we don’t
reject the entire theory outright; the model is refined
to accommodate new data.” Saunders then goes on
to rubbish the idea that “there is a mafia out
to silence the anti-plume lobby”.
Saunders rejects the idea that plumes
are not supported by evidence — he says that seismic
tomography, which can map the speed of seismic waves
through rocks, shows that the waves slow down beneath
Hawaii, a so-called hotspot (Iceland and Yellowstone
National Park are other examples of hotspots).
This suggests, according to Saunders,
the existence of an upwelling of buoyant, probably hot,
rock beneath the island, which fits with his working
definition of a plume. “If it was not for this
plume, we wouldn’t have Hawaii,” he concludes.
Foulger has suggested the island may have resulted from
a tear in the plate — Saunders says it is theoretically
possible, but that no such puncture has been observed.
Why should the debate have become so
impassioned? “I don’t know,” Saunders
says. “Sometimes it looks good to be an iconoclast.
If you are proven right, you are seen as a forerunner
in the brave new world. Perhaps people are just frustrated
with what is a very old model. A lot of the evidence
“These things are happening where
you can’t see them. But you cannot see the Earth’s
core, and nobody is saying it does not exist.”