Alfred Wegener Scientist or Pseudoscientist?

VisionaryAlfred Wegener's greatest contribution to the scientific world was his ability to weave seemingly dissimilar, unrelated facts into a theory, which was remarkably visionary for the time. Wegener was one of the first to realize that an understanding of how the Earth works required input and knowledge from all the earth sciences.

Alfred Wegener Biography

Wegener's scientific vision sharpened in 1914 as he was recuperating in a military hospital from an injury suffered as a German soldier during World War I. While bed-ridden, he had ample time to develop an idea that had intrigued him for years.

Like others before him, Wegener had been struck by the remarkable fit of the coastlines of South America and Africa. But, unlike the others, to support his theory

Alfred Wegener Biography

Wegener sought out many other lines of geologic and paleontologic evidence that these two continents were once joined. During his long convalescence, Wegener was able to fully develop his ideas

into the Theory of Continental Drift, detailed in a book titled Die Entstehung der Kontinente und Ozeane (in German, The Origin of Continents and Oceans) published in 1915.

Alfred Wegener Biography

Wegener obtained his doctorate in planetary astronomy in 1905 but soon became interested in meteorology; during his lifetime, he participated in several meteorologic expeditions to Greenland. Tenacious by nature, Wegener spent much of his adult life vigorously defending his theory of continental drift, which was severely attacked from the start and never gained acceptance in his lifetime. Despite overwhelming criticism from most leading geologists, who regarded him as a mere meteorologist and outsider meddling in their field, Wegener did not back down but worked even harder to strengthen his theory

Wegener's theory

Based in part on what appeared to him to be the remarkable fit of the South American and African continents, first noted by Abraham Ortelius three centuries earlier. Wegener was also intrigued by the occurrences of unusual geologic structures and of plant and animal fossils found on the matching coastlines of South America and Africa, which are now widely separated by the Atlantic Ocean. He reasoned that it was physically impossible for most of these organisms to have swum or have been transported across the vast oceans. To him, the presence of identical fossil species along the coastal parts of Africa and South America was the most compelling evidence that the two continents were once joined.

Continental Drift

Ideas of Alfred Wegener• Fit of Africa and South America• Features common to southern continents:

– rock types and ages– Glaciation of late Paleozoic age– Similar Permo-Triassic fossils

• Plants - Glodsopteris• Reptiles - Mesosaurus

Major Physical Features of Earth

Fig. 1.13

Physical Features of the Earth

Land of 200 Million Years Ago

Fit of South America and Africa

Permian Glaciation

Long swim for Mesosaurus

Why they didn’t have to swim or float

Continental Drift Ideas of Alfred Wegener

• Paleo-Climatic evidence

- Either continents had a different orientation with respect to the poles in the

past.

• Or, the poles have wandered.

Wegener’s Downfall: Lack of a Mechanism

• Support from the southern continents• Some acceptance in Europe• Almost total skepticism in N.A.• Condemnation by American geophysicists.

NO MECHANISM!!!

Alfred Wegener"Utter, damned rot!" said the president of the prestigious American Philosophical Society. "If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again," said another American scientist. Anyone who "valued his reputation for scientific sanity" would never dare support such a theory, said a British geologist. Thus did most in the scientific community ridicule the concept that would revolutionize the earth sciences and revile the man who dared to propose it, German meteorological pioneer and polar explorer Alfred Wegener. Science historians compare his story with the tribulations of Galileo.

The Wrath of Science

The international geological community's reaction to Wegener's theory was militantly hostile. American geologist Frank Taylor had published a similar theory in 1910, but most of his colleagues had simply ignored it. Wegener's more cogent and comprehensive work, however, was impossible to ignore and ignited a firestorm of rage and rancor. Moreover, most of the blistering attacks were aimed at Wegener himself, an outsider who seemed to be attacking the very foundations of geology.

Wegener’s Proposed MechanismsWhy do the continents “plow around on the earth’s mantle”?

• The tides move the continents.

• Centrifugal force from the earth spinning. “Flight from the poles”

• "It is probable the complete solution of the problem of the forces will be a long time coming," he predicted in his last (1929) revision.

• Bottom line, there was no reasonable mechanism.

Testimonials

Wegener noted, however, that one thing was certain:

“The forces which displace continents are the same as those which produce great fold-mountain ranges. Continental drift, faults and compressions, earthquakes, volcanicity, [ocean] transgression cycles and [apparent] polar wandering are undoubtedly connected on a grand scale.”

Wegener's final revison cited supporting evidence from many fields, including testimonials from scientists who found his hypothesis resolved difficulties in their disciplines much better than the old theories.

Fossil and Geological EvidenceFossils and geologic evidence show that most of the continents used to have startlingly different climates than they do today. Wegener thought continental drift was the key to these climatic puzzles, so he and Vladimir Koppen plotted ancient deserts, jungles, and ice sheets on paleogeographic maps based on Wegener's theory. Suddenly the pieces of the puzzles fell into place, producing simple, plausible pictures of past climates. Evidence of the Permo-Carboniferous ice-age era that peaked some 280 million years ago, for example, was scattered over almost half the Earth, including the hottest deserts. On Wegener's map, however, it clustered neatly around the South Pole—because Africa, Antarctica, Australia, and India had once comprised a Southern Hemisphere supercontinent (Gondwanaland).

Geopoetry

• Unfortunately, though Wegener's explanation of the Permo-Carboniferous ice age impressed even his critics, the merit of much of the rest of his supporting evidence was not widely recognized at the time. As a result, most geologists eventually dismissed his theory as a fairy tale or "mere geopoetry."

Why is Continental Drift/Plate Tectonics Accepted Today?

• Is it because scientists suddenly became more open minded? NO!!!!

• It is because new evidence emerged which strongly supports his theory.

• It is because a believable mechanism emerged.

Paleomagnetism and the Revival of Continental Drift

Nature of Paleomagnetism•Magnetism a property of iron- bearing minerals.•If permitted to do so, these grains align parallel to earth’s magnetic field.•Records position of earth’s magnetic poles.•Determined in laboratory from field samples.

Paleomagnetism, etc.Results of Paleomagnetic

Studies

• Plotting position of pole based on North American data shows an apparent

wandering through time.

• 13,000 MILES TO PRESENT POSITION IN ARCTIC CIRCLE.

Polar Wandering ?

**

*

*

**

The symbol

shows the

path of the

NMP from

Precambrian

To Cretaceous.

PaleomagnetismResults

• However, the position of the pole from European data does not match that of the data from North America.

• Indeed, each continent appears to have its own path for polar wandering.

• Because this is impossible, continents must have been moving about during this time.

• Only recently have they moved to the present position.

Evidence from the Oceans• World War II brought a spectacular

advance in our abilities to study the ocean.• Among the discoveries were:

– Heat-flow measurements– Thickness of the oceanic crust– Thickness and age of sedimentary deposits on

the ocean floor.– Earthquakes along ridges, trenches.– Very large fractures, most of them faults.

Exploring the Ocean Floor

Hypothesis of Sea-Floor Spreading

• Convection currents in mantle rise under oceanic ridges and spread.

• Driving force is here transferred from core to mantle.

• Oceanic crust (basaltic) created at ridges.• Crust plus upper mantle (lithosphere) move

laterally away – going along for the ride.

Hypothesis of Sea-Floor Spreading

Sea-Floor Spreading • Lithosphere plunges into oceanic trenches.

Does this explain the anomalies of ocean floor heat distribution?

• Continents don’t drift through the mantle but are passengers.

• Oceanic crust has to be young because older rocks have been:– Plastered onto the edge of continents.– Thrust down into the mantle.

Why are the sedimentary materials on the ocean floor so thin?

Confirmation of Sea-Floor Spreading

• Earth’s magnetic field periodically reversed.

• The age of these reversals determined by radiometric dating.

• Magnetic anomalies found on both sides of oceanic ridges.

• Preserved in basalt formed in center of rise.

Magneticanomalies

Confirmation of Sea-Floor Spreading

Confirmation of Sea-Floor Spreading

• Through sea-floor spreading, sea floor has served as a tape recorder – working in stereo.

• Preserved record of reversals and their time of occurrence.

• Can also determine rate of spreading.~ 1 inch per year in North Atlantic~ 2 inches per year in South Pacific

Plate TectonicsBasics

• Earth’s lithosphere broken into large plates.

• Upwelling of magma creates new oceanic crust. Added to edge of plate.

• Plates diverge from ridge.

• Elsewhere, plates

– Pass into oceanic trenches (subduction).

– Collide with each other.

– Push past each other along great strike-slip faults.

PlateBoundaries

Convergent Plate Boundaries

Plate Tectonics• Collisions can involve an oceanic plate and

a continental plate, two continental plates, or two oceanic plates.

• Continents do not drift, but are rafted about.

• Some oceanic basins are steadily widening; others are closing.

• Driving mechanism believed to be convection currents of some type.

Hypotheses About Convection Cells

Plate Tectonics

• Benioff zones: long narrow earthquake zones dipping into the lithosphere.

• Created by rupture of subducting plate.• Hot spots where plumes of magma rise from the

asthenosphere.– Remain fixed– Plate migrates over, creating chain of

volcanoes.

Hawaii, Yellowstone

•Continental Rifting

Vindication

Some of the earliest evidence confirming Wegener's theories of continental drift was revealed when geologists measured the age of the ocean floor. Crustal rocks near the mid-ocean ridges are always very young, while the ocean crust along continental margins, furthest away from the ridges, is hundreds of millions of years older. New ocean floor is being created at the mid-ocean ridges—pushing the continents along