Dennis McCarthy /Der Spiegel on JGR paper
Here Be Dragons (Oxford University Press)
Researcher reveals secret of the northerly drift
By Axel Bojanowski / Spiegel Online
Researchers have overlooked it for many decades: The crowding of the continents in the northern hemisphere can be
explained with simple global geometry - and with a tectonic spreading ring around Antarctic. The insight comes so late
because scientists look so rarely at the bottom of the earth.
Some questions are so good and so simple that only children ask them. Thus, for example, no scientist was surprised at the
fact that almost all continents lay on the north hemisphere of the earth, while the southern hemisphere is covered
predominantly by oceans -- although this really jumps at the eye of everyone who looks at a globe.
Up to now, however, geo-researchers had explained it with silly plausibility-answers: The drift of the earth's plates has created
this pattern just by chance. This sounds unsatisfactory as an explanation, and the real reason has been a long time coming.
Now a researcher of a natural history museum provides a better answer: The unequal distribution lies in the shape of the
earth – and in a powerful, all too evident motive force that other geo-researchers had overlooked like the proverbial forest for
the trees. Dennis McCarthy, at the museum of Science in Buffalo, New York discovered the answer by regarding the globe
from an unusual perspective: from below.
Antarctica lies on the South Pole of the planet, thousands of kilometers away from other dry little spots --- a special case
below all the other land masses. Because a three kilometer high spreading ridge in the seafloor surrounds the south
continent, lava perpetually pours from this so-called mid-oceanic ridge and hardens to form new earth crust. This pushing
lava continually forces the plates apart.
THE NORTHWARD PUSH
But around the submarine spreading ridge the tectonic plates all push mutually, hence, Antarctica remains relatively
stationary. And the pressure must be released northwards. There the new seafloor and the circum-Antactic ridge moves.
Consequently, all the plates all around the south continent are pressed toward the equator.
The northern drift and the shape of the earth cause the differences between the northern hemisphere and southern
hemisphere, McCarthy has found out: Just as degree of longitudes lie further apart at the equator than near the Pole, the
northward moving plates have also diverged. Therefore, the seafloor of southern hemisphere rips apart. There new seafloor
continuously forms - [and] the oceans of the south become larger, writes McCarthy now in the renowned specialist journal
"Journal of Geophysical Research".
Bojanowski's article on the JGR paper has also appeared in
SonntagsZeitung, a nationwide Sunday paper of Switzerland
2. Part: Humans have distorted, mutilated, and ignored Antarctica on maps -- thus they also overlooked the obvious engine for the northern drift of the continents.
The spherical shape? How trivial! However, maps shape world views, and the troubles that humans have had in modeling the three-dimensional world adequately on a level surface have
stretched throughout the history of the modern age. Antarctica always became the first victim of cartographers: absurdly distorted as disproportionate strips in the lower map edge - or
completely left out. So as a fulcrum and pivot of plate tectonics, Antarctica and her undersea spreading ridges did not attract attention.
That is the problem of perspective, says the geologist Helmut Echtler of the geo research center potsdam (GFZ) to MIRROR ON-LINE ONE: Due to its peripheral location on the maps, one
considers the south continent too infrequently.
THE GREATER ROOM AT THE EQUATOR
All the necessary data were present. McCarthy used a standard geological map ("Nuvel-1") with motion and velocity of the plates as determined by GPS measurements, and are available
to every researcher. The plates move in all directions. However, McCarthy put down the vectors precisely into tables - and discovered: In general, the earth plates move northward more
than in any other direction.
The earth plates [move] away from Antarctica to the north, McCarthy has calculated. The cause is the spherical shape of the earth: In the southern hemisphere, the pushing seafloor has a
lot of room and can move nearly without braking [toward the equator], explains McCarthy.
Over the course of the last 200 million years, most continents were pushed thus in the northern hemisphere. Now large crowding thus prevails there, and the plates collide in many
places: A collision front stretches, for instance, from Europe to Eastern Asia, along which mountains tower up like the Alps and the Himalayas. As the spur land masses – like Africa and
India - push into the Eurasian continent from the south, collisions slow the plates in the northern hemisphere, McCarthy has calculated.
"ELEGANT GEOMETRICAL EXPLANATION"
The study surprises the professional world. The work shows that the movement of the tectonic plates can be explained elegantly with geometry, says Onno Oncken, GFZ expert for
Plattentektonik, to SPIEGEL ONLINE. Up to now plate movements were reconstructed only with the help of measured motions.
Now McCarthy's geometry law possibly explains even [past and future configurations of] the continents. Since in the course of the history of the earth the land masses united several times
to a supercontinent. Why this happened appeared puzzling for a long time.
According to the new study, the plates conglomerate possibly systematically : The last supercontinent Pangea – before 225 million years ago -- comprised almost all of the land mass of
the earth and partially lay on the south hemisphere -- disintegrated before about 200 million years ago. The break-up originated [at least in part] as a result of that exact same undersea
spreading ridge around today's Antarctica, which has driven the tectonic plates to the north since that time.
In the distant future today's continents will presumably join in the north, says the geologist Wolfgang Frisch of the University of Tübingen to SPIEGEL ONLINE. He is the author of the
standard work "Plattentektonik". The next continent cycle would possibly begin when another huge lava ring opened near the North Pole. Following McCarthys geometry rule, Frisch
speculates: Then the continental plates could drift again toward the south - and in the north an enormous new ocean would develop.