Biography alfred wegener & harry hess



Yüklə 34,83 Kb.
Pdf görüntüsü
tarix13.12.2017
ölçüsü34,83 Kb.
#15163


BIOGRAPHY

ALFRED 

WEGENER & 

HARRY HESS

4

780L




By Cynthia Stokes Brown, adapted by Newsela

Alfred Wegner

Born

November 1, 1880

Berlin, Germany

Died

November 1930

Clarinetania, Greenland

Harry Hammond Hess

Born

May 24, 1906

New York, New York

Died

August 25, 1969

Woods Hole, Massachusetts

CONTINENTS 

IN MOTION 

ALFRED 

WEGENER & 

HARRY HESS



2

 3

Alfred Wegener showed  



evidence in 1912 that 

the continents are moving. 

But, geologists rejected 

his ideas at first, partly  

because Wegener wasn’t 

a geologist. He also couldn’t 

explain how the continents 

moved. Almost 50 years 

later, Wegener’s ideas 

were confirmed. Harry 

Hess proved Wegener right 

by using evidence that 

the ocean’s floor spreads 

to explain what moved the  

continents.



4

 5

Balloons and Arctic air



Alfred Wegener was born in Berlin, Germany. He received a PhD in astronomy 

from the University of Berlin in 1904. However, his real love was air bal-

loons. He and his brother, Kurt, set the world’s record in 1906 for the longest 

time spent in a balloon — 52 hours. 

Later that year, Wegener joined an expedition to Greenland. He would use his 

expertise with air balloons to track polar air circulation. Wegener had always 

dreamed of polar exploration. 

Continental drift

Wegener studied the atmosphere as a meteorologist. He was earning rec- 

ognition for his work. Yet his mind kept roaming. By 1910, he had noticed  

on a map that the east coast of South America fits exactly against the  

west coast of Africa. It appeared as if they had once been joined. He found  

evidence that it had and, in 1915, published The Origin of Continents and 

Oceans. In it, he claimed that about 300 million years ago, the continents 

formed a single mass. He labeled it “Pangaea,” a Greek word meaning 

“whole Earth.”

Wegener was not the first to present the idea of “continental drift.” But he 

beat everyone else in putting together evidence from different scientific  

approaches. He found fossil evidence showing that the Earth was once one 

land mass. For instance, he located ancient tropical plants on the Arctic  

island of Spitzbergen. This is thousands of miles from where you would  

expect to find them.

Wegener also found rocks and mountains on different continents that were 

similar. He pointed out that the Appalachian Mountains in the U.S. are similar 

to the Scottish Highlands. He located rock layers called “strata” in South 

Africa that matched those in Brazil. 

Scientists then believed that land bridges had once connected the continents. 

The theory was that they later sunk into the ocean. Wegener wanted to end 

that theory. He also disputed the theory of the time that mountains formed 

like wrinkles on the skin of a drying apple. Instead, he claimed that mountains 

formed when the edges of drifting continents collided and crumpled. Later 

studies backed up Wegener’s research. Scientists now believe India hit Asia, 

creating the Himalayas. 

Geologists mocked Wegener’s ideas. Wegener was not even a geologist.  

Who was he to try to overturn their beliefs?

Besides, he couldn’t explain what caused the continents to plow through  

the Earth’s crust. It would have required immense force. Picture ice-breaking 

ships cutting through frozen sheets of ice, just vastly more powerful.

In 1930, Wegener led another expedition to Greenland. He set up weather-

monitoring equipment at stations on the glacier.

Alfred Wegener considers weather data at his desk in Greenland, 1930



6

 7

In November 1930, Wegener led dogsled teams carrying supplies to his  



colleagues at an isolated weather station. He celebrated his 50th birthday  

at the station. On his return trip back to the coast, Wegener died. 

Seafloor spreading

Scientists kept talking about the idea of continental drift. During World War 

II, sounding gear produced new evidence of what the seafloor looked like. 

The gear, called sonar, was developed in the 1930s. It worked by bouncing 

sound waves off the seafloor. Sonar equipment on board received the waves 

and determined the seafloor’s depth and features.

It happened that a geologist from Princeton University named Harry Hess 

was put in charge of a military ship. Hess wanted to continue his scientific 

investigations even while at war. Ship commanders usually turned on 

sounding gear to navigate when docking. Hess, however, left his ship’s gear 

on all of the time.

What Hess discovered was a big surprise. The bottom of the sea was not 

smooth as expected. It was, in fact, full of canyons, trenches, and volcanoes. 

By the 1950s, other researchers had found that a huge rift ran along the  

top of the Mid-Atlantic Ridge. The discovery enabled Hess to understand 

what he’d learned about the ocean floor of the Pacific. He now knew that  

the Earth’s crust had been moving away on either side of oceanic ridges. 

The ridges ran down the Atlantic and Pacific oceans. They were long —  

and volcanically active. He published his theory in 1962. It came to be called 

“seafloor spreading.”

In the early 1960s, samples were taken from deep in the ocean’s floor and 

dated. They showed that the ocean floor was younger at the Mid-Atlantic 

Ridge. It became older and older in either direction. This confirmed that the 

seafloor was truly spreading. Further evidence came along by 1963. Geo-

physicists realized that Earth’s magnetic field had reversed polarity many 

times. Each reversal lasted fewer than 200,000 years. When this happened, 

the North Pole and South Pole swapped magnetization. 

Rocks on the seafloor would show the magnetic polarity at the time that that 

part of the crust formed. Sure enough, rocks were found in the Mid-Atlantic 

Ridge. They had a pattern of alternating stripes of polarity. It’s almost like a 

zebra’s coat. That clinched the argument for most geologists.

Unlike Wegener, Hess lived to see his major theory accepted. He helped to 

plan the U.S. space program. On August 25, 1969, he died of a heart attack.  

It was just a month after the Apollo 11 mission brought the first humans to 

the Moon.

Harry Hammond Hess




8

 9

Plate tectonics



By the 1970s, geologists had agreed to use the term “plate tectonics.” They 

already knew that the continents move. But, they’d also found evidence that 

so do whole “plates” of the Earth’s crust. A plate might include a continent 

or parts of a continent. Even portions of the Earth’s crust now underwater 

can form plates. Wegener’s idea of continental drift had been taken a step 

further.


Geologists today understand that the Earth’s crust is broken up into eight  

to 12 large plates and 20 or so smaller ones. These plates move in different 

directions and at different speeds. Their sizes don’t match the landmasses 

on top of them. For instance, the North American plate is much larger than 

the North American continent. The plate starts at the western coast of  

North America. Yet, it extends into the middle of the Atlantic Ocean. Iceland 

is split down the middle. It belongs to two different plates.

The continents have come together into one large mass — and then split 

apart again — more than once. Over the last 500 million years, this may 

have happened as many as three times.

The force that moves the plates is thought to be convection currents in the 

Earth’s mantle. The mantle is the area below the Earth’s crust. It separates 

the earth’s core from the crust. The mantle is solid in the short term.

But over longer geologic time, the mantle does flow, though very slowly. And 

plates float on top of the mantle. Pockets of hot liquid magma in the mantle 

ooze up along mountain ridges deep under the water. One runs north-south in 

the middle of the Atlantic Ocean. Another runs in the mid-Pacific Ocean.

Along these ridges are active volcanoes and hot-water vents. Very hot, miner-

al-rich water pours through these vents. The water nourishes amazing forms 

of life. These ecosystems are the only ones on Earth that live without sun- 

light. It’s possible that the first living things on Earth developed in such vents.

Where the edges of the plates meet, several things may happen. Continents 

are lighter than the ocean floor. So, if both plates carry continents, they  

may clash head on. Mountains rise up at the point of collision. If one plate is 

heavier, it may go under the other, a process known as “subduction.” The 

part of the plate that gets subducted becomes part of the mantle. 

Or the plates may grind against each other. As they grind together, cracks, 

or faults, appear in the plates. However plate edges meet, earthquakes take 

place. If you look at a global map of earthquake zones, the outlines of the 

plates are clearly visible.

The European and North American plates are moving apart at the speed  

a fingernail grows. In a human lifetime, this amounts to about two meters  

(just over six feet). Millions of years in the future, parts of California and 

Mexico will probably drift off. They’ll separate from North America and  

become an island.

Most of Africa is pushing toward Europe. Eventually, it will squeeze out the 

Mediterranean Sea. When it reaches Europe, it will cause high mountains  

to form along the southern coast. The eastern portion of Africa will split off 

at the Great Rift Valley. It will then float off into the Indian Ocean. In slow 

geologic time, the Earth’s plates are always moving.

A map of the tectonic plates of the world



 11

10

Sources



Bryson, Bill. 

A Short History of Nearly Everything. New York: Broadway 

Books, 2003.

Image credits

Alfred Wegener, 

courtesy of the Alfred Wegener Institute for Polar and Marine Research 

Alfred Wegener considers weather data at his desk in Greenland, 1930,  

courtesy of the Alfred Wegener Institute for Polar and Marine Research 

Harry Hess, 

courtesy of Princeton University Archives 

Plate tectonics map, 



United States Geologic Survey (USGS)

Articles leveled by Newsela have been adjusted along several dimensions of text complexity including  

sentence structure, vocabulary and organization. The number followed by L indicates the Lexile measure  

of the article. For more information on Lexile measures and how they correspond to grade levels:  

http://www.lexile.com/about-lexile/lexile-overview/

To learn more about Newsela, visit www.newsela.com/about.

The Lexile

®

 Framework for Reading

The Lexile

®

 Framework for Reading evaluates reading ability and text complexity on the same developmental 

scale. Unlike other measurement systems, the Lexile Framework determines reading ability based on actual 

assessments, rather than generalized age or grade levels. Recognized as the standard for matching readers 

with texts, tens of millions of students worldwide receive a Lexile measure that helps them find targeted  

readings from the more than 100 million articles, books and websites that have been measured. Lexile measures 

connect learners of all ages with resources at the right level of challenge and monitors their progress toward 

state and national proficiency standards. More information about the Lexile

®

 Framework can be found at 

www.Lexile.com.

Yüklə 34,83 Kb.

Dostları ilə paylaş:




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©genderi.org 2024
rəhbərliyinə müraciət

    Ana səhifə