Plate Tectonics Archives - Eva Varga

November 1, 2015

Ever since the continents were all mapped, people had noticed that many coastlines, like those of South America and Africa, looked as though they would fit together if they could be moved like puzzle pieces.

Alfred WegenerWith his revised publication of The Origin of Continents and Oceans in 1915 (originally published three years prior), Alfred Wegener was one of the first to suggest continental drift and plate tectonics. In his work, he described a ‘super-continent’ he called Pangaea had existed in the past, broke up starting 200 million years ago, and that the “pieces drifted” to their present positions. Citing similar ancient climates, rock structures, and fossil evidence.  [ Frank Taylor, an American scientist, had published a similar theory in 1910 but his work attracted little attention. ]

When continental drift was first proposed by Alfred Wegener in the early 1900s however, it was met with skepticism by the scientific community. The proposal remained controversial until the 1960s, when it became widely accepted over a fairly short period of time. Today, the theory of plate tectonics is key to the study of geology.

However, Wegener is not only the father of the theory of continental drift, he was also the first to describe the process by which most raindrops form. This process is now called the Wegener-Bergeron-Findeisen procedure.

The Pangea Puzzle, Ice Halos, & Raindrops: The Influence of Alfred Wegener

Photo by Greg Clements (Field Studies in Greenland)

During Wegener’s lifetime the process by which cloud particles reach raindrop size was not known, but there was some idea how much rain, even during summer, began as snow in the clouds. In 1784, Benjamin Franklin had suggested this, and in 1904, Wilson A. Bentley, who spent a lifetime studying snow crystals and raindrops, found supporting evidence for the conjecture.

“Perhaps the only thing that saves science is the presence of mavericks in every generation.” ~ Alfred Wegener

In his 1911 publication, The Thermodynamics of the Atmosphere, Wegener noted that ice crystals invariably grow at the expense of super-cooled droplets because the crystals have a lower equilibrium vapor pressure. He then suggested that raindrops might result from this competition between ice crystals and super-cooled cloud droplets. Read more in the article Introducing Precipitation from the Eyewitness Companions: Weather from DK Publishing.

Wegener had hoped to document this process in real clouds, but other projects intervened and he never returned to the subject. Thus, it was left to Tor Bergeron and W. Findeisen to develop and prove the theory in the 1930s.

He also explained two rare ice crystal halo arcs that bear his name as well. Ice crystals often form in the frigid air just above the Greenland ice cap and can produce spectacular halos. In a 1926 article, Wegener explained two relatively rare arcs that appear opposite the sun and are now named in his honor.


The Pangea Puzzle: The Impact of Alfred Wegener @EvaVarga.netBorn in Berlin on November 1st, 1880, Alfred Wegener, was a German climatologist and geophysicist.

From an early age he took an interest in Greenland. He studied in Germany and Austria, receiving his PhD in astronomy in 1904. No sooner did he finish his dissertation than he dropped astronomy to study meteorology, the new science of weather.

At a time when the conquest of the North and South Pole began to enjoy enormous international public attention, Wegener made his first expedition to Greenland as the official meteorologist on a two-year Danish expedition in 1906.

Wegener experimented with kites and balloons, pioneering the use of balloons to track air circulation. That same year, he and his brother Kurt set a world record in an international balloon contest, flying 52 hours straight. When he returned he took up teaching meteorology at the University of Marburg.

He was the first to use kites and tethered balloons to study the polar atmosphere.

His fourth and final expedition was in 1930 as the leader of a major Danish expedition to Greenland. He celebrated his fiftieth birthday on November 1, but shortly afterwards the team got separated, and he was lost in a blizzard. His body was found halfway between the two camps.

The Pangea Puzzle: The Influence of Alfred Wegener @EvaVarga.netBring it Home

Science MilestonesVisit my Science Milestones page to learn more about scientists whose discoveries and advancements have made a significant difference in our lives or who have advanced our understanding of the world around us.

September 18, 201414

modeling plate tectonicsThe theory of plate tectonics provides geology with a comprehensive theory that explains how the Earth works. Though Alfred Wegener was the first to suggest the theory of continental drift and plate tectonics in 1915, it wasn’t widely accepted until the 1960s and 1970s as new information was obtained about the nature of the ocean floor, Earth’s magnetism, the distribution of volcanoes and earthquakes, the flow of heat from Earth’s interior, and the worldwide distribution of plant and animal fossils.

The theory of plate tectonics states that the Earth’s lithosphere is broken into 15 major plates.  Seven large plates include: the African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates.

These plates are all moving in different directions and at different speeds (from 2 cm to 10 cm per year–about the speed at which your fingernails grow) in relationship to each other atop the hot plastic upper mantle, known as the asthenosphere. These plates are in motion as a result of convection in the asthenosphere, creating a variety of interactions at the plate boundaries. At the plate boundaries, plates may converge (collide), diverge (separate), or slide past each other (transform boundary).  In addition, some plates may appear to be inactive.

In this simple activity, students will model each of the different types of interactions at plate boundaries. Each pair of students will need the following materials:

4 squares of graham crackers
1/2 rice cake
4 dollops of frosting
a small dish of water
paper plate

Part 1: Divergent Plate Boundaries

1.  Divide your plate into four sections with a marker
2.  Place a dollop of frosting in each quadrant
3.  Lay the two pieces of graham cracker side by side on top of the frosting so they are touching.
4.  To imitate the result of diverging oceanic plates, press down on the crackers as you slowly pull apart in opposite directions.

Think About It
1.  What do the graham crackers represent?
2.  What does the frosting represent?
3.  What happened to the frosting between the crackers?
4.  Name a specific location on the Earth where this kind of boundary activity takes place.
5.  What type of feature is produced by this movement?
6.  What is the process called that creates new ocean floor from diverging plates?

Part 2: Convergent Plate Boundaries (Oceanic & Continental –> Subduction)

1.  Take another graham cracker (to represent the thin but dense oceanic plate) and lay it next to a rice cake (to represent the thicker but less dense continental plate) so they are almost touching, end to end.
2.  Push the two “plates” slowly toward each other and observe which plate rides up over the other. On the actual surface of the Earth, the oceanic plate is subducted.

Think About It
1.  Why does the oceanic plate sink beneath the continental plate?
2.  Name a specific location on the Earth where this kind of boundary activity takes place.  Look at the attached plate tectonics diagram for help.
3.  What features are formed on the continent along this boundary?
4.  What feature is formed in the ocean along the subduction zone?

plateboundariesPart 3: Convergent Plate Boundaries (Continental –> Mountains)

1. Take two new graham crackers. Each piece of graham cracker represents a continental plate.
2. Dip one end of each of the two graham crackers into a cup of water. Don’t wait too long or they will fall apart.
3. Immediately remove the crackers and lay them end to end on the frosting with the wet edges nearly touching.
4. Slowly push the two crackers together.

Think About It
1. What happens to the wet ends of the graham crackers?
2. What feature do the resulting ends of the wet crackers represent?
3. Name a specific location on the Earth where this type of boundary activity takes place. Look at the plate tectonics diagram for help.

Part 4: Transform Plate Boundaries (Sliding)

1. Take two graham cracker pieces and lay the two pieces side by side on top of the frosting so they are touching.
2. Place one hand on each of the graham cracker pieces and push them together by applying steady, moderate pressure. At the same time, also push one of the pieces away from you while pulling the other toward you.

* If you do this correctly, the cracker should hold while you increase the push-pull pressure, but will finally break from the opposite forces. We found this one the most difficult to model accurately. 

Think About It
1. Name a specific location on the Earth where this type of boundary activity takes place. Look at the attached plate tectonics diagram for help.
2. Nothing happens at the beginning, but as the pressure is increased, the crackers finally break. What do we call the breaking and vibrating of the Earth’s crust?
3. Why do you think Earthquakes typically occur in California and not in the midwest?