Alfred Wegner (1880- 1930) was a radical pioneer, advancing
scientific thinking though thorough research and critical observations. His
ideas created a ‘stepping stone’, literally and metaphorically, which brought
continents together and progressed ideas of the world in leaps and bounds. However, it was not until after his death
that his ideas were accepted by the scientific community.
Right from the start, Wegner was always going to struggle to
achieve acceptance of his theories. Being a meteorologist, and not a geologist,
meant that many did not appreciate his scientific understanding and did not
feel he was qualified to theorise on Earth’s past. Wegner was dogged though. He had an idea and
he couldn’t let go of it: that the continents had once all been connected as
one super continent, Urkontinent (German for one continent).
It’s easy to see why he came up with this idea. Looking at
the edges of the continents they appear like pieces of a puzzle. The Western
side of South America fits neatly into the bite out of the east coast of
Africa. America and Europe can be slotted together at a bit of an angle. The
jigsaw fit of the continents was Wegner’s first piece of evidence to support
his theory of Continental Drift, where he proposed the continents were drifting
apart and had once been together.
Wegner was a smart man and an excellent scientist. He knew
that a simple observation like that would never ensure his theory would be
accepted. He needed more evidence. So, the meteorologist turned his hand to
palaeontology -the study of fossils. The Mesosaur was the first fossil to
assist him with his radical ideas. A freshwater reptile which couldn’t survive
in salt water, was found on both sides of the Atlantic, in South America and
Africa. There was no way this creature could have swam, and it definitely
didn’t fly. This was surely evidence that these land masses were once
joined. Further studies into other
fossils began to show similar findings, where organisms which had no means of
crossing large oceans appeared to have done just that.
Wegner was on mission. He travelled the globe and found
further evidence in the rocks. The Appalachian Mountains of the east coast of
North America were found to be geologically the same as rocks found on British
and Scandinavian coasts. These were later dated and found to be the same age as
well. A coincidence? Surely not!
On an expedition to Svalbard in Norway, Wegner found fossils
of tropical plants which indicated a much warmer climate in the past. Had
Norway once been closer to the equator? Still thinking along these lines,
Wegner noted that bituminous coal, which typically forms in tropical forests
and swamps, could be found in the northern hemisphere as well as Antarctica, far
from where you would expect coal to form now. Travels to Africa and South America
delivered more insight. On the rocks he
found scratches, known as glacial striations. These are caused when glaciers
move over the land. Had these now warm continents once been much colder?
Wegner compiled his evidence in a book, The Origins of
Continents and Oceans. However, without a mechanism to explain what caused
continents to move, his ideas were still quashed. In his search for further
proof, Wegner travelled to the Antarctic and was lost in a blizzard. Wegner
died before a mechanism for these continental movements was found, and thus
never saw his theory accepted by the scientific community, and with no
appreciation of the fantastic research he had pulled together.
Current thinking
It is now widely accepted that the continents did once fit
together as one supercontinent (we now call Pangea which is Greek for All
Earth). In fact, there is evidence that the continents have come together and
pulled apart at least three times in Earth’s history.
However, unlike Wegner’s idea that they “drift” like rubber
ducks on a pond, tectonic plates are forced to move slowly, driven by processes
within the Earth. Our understanding of these processes is still evolving with
time but forms part of the Theory of Plate Tectonics. Most people will have
learnt that convection currents within the mantle push the plates apart at mid-ocean
ridges, and together at collision or convergent zones (resulting in subduction
and/or mountain building, depending on the plates involved). However, more
recent ideas, from newer evidence of processes, are that slab-pull, where the
subducting edge of a plate drags the rest of the plate downwards is a major driving
force of plate tectonics.
One of the most exciting things about Geology is that there
is so much still to learn, and so many questions yet to be answered. Theories
are still being questioned today, and we need the radical thinkers and Wegner’s
of the world to continue to work doggedly to propose answers and gather
evidence.
Webpages
- For more information and activities relating to plate tectonics check out the Year 9 WASP resources.
- For more information about current thinking on the driving force behind plate tectonics read this article by the British Geological Survey.
Video
- For a short video about Alfred Wegner’s Theory, featuring a fun activity, click here.
References: All
images from wikicommons