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Transcript for "Expedition Panama"

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Bridge That Changed the World

For most of Earth's history, the Isthmus of Panama did not exist. Once it formed and connected the continents of North and South America, the new land bridge produced global consequences. The oceans on either side of the isthmus changed. Currents flowed differently. Animals began migrating north and south. Climates changed and new species evolved. In the words of STRI Deputy Director Tony Coates, "It was the greatest event since the death of the dinosaurs."

Curriculum Links
Put a Spin on Ocean Currents
Activity 1: Linear Speed and the Earth
Activity 2: It's All in the Timing






Central America,

climate, ecology,
ocean currents


linear speed,
rotational speed

Coriolis effect


The emergence of the Isthmus of Panama four million years ago had global consequences. The new isthmus blocked the flow between the Atlantic and Pacific oceans. As a result, the currents in the Atlantic began to flow northeast to form the Gulf Stream. But why did the water movements form a clockwise current system in the North Atlantic? Why didn't the blocked current flow southeast and produce a counterclockwise flow? By understanding the phenomenon known as the Coriolis effect, you will be able to answer these questions. The Coriolis effect does not create currents, but it does cause them to flow in a particular direction. Once the isthmus blocked the flow, the spinning Earth caused ocean currents to deflect to the right in the Northern Hemisphere and deflect to the left in the Southern Hemisphere.

A difference in linear speeds produces the Coriolis effect. You can measure linear speeds at different places on the planet and discover this differential for yourself. Remember that every place on Earth has the same rotational speed -- it takes 24 hours to make one complete rotation. So points on Earth that have a longer distance to travel go faster. For example, the linear speed of San Francisco is 810 miles per hour, but in Nome, Alaska, it's 360 miles per hour. In Activity 1: Linear Speed and the Earth, you will perform simple calculations to compare linear speeds as you learn how Earth's rotation puts a spin on current flow.



Investigate the effects of Earth's rotation.

  • string
  • globe
  • ruler
  1. Wrap a section of string around the equator of a globe. Measure this string against the scale presented on the globe to determine the length of the equator. (If 2" = 1 mile and the string length is 10", then the length would be 5 miles.) Record the length.

  2. Find the location of your town or a nearby city on the globe. Identify its latitude and use a string to measure the length of this latitude line as it encircles the entire globe. Use the globe's scale to determine the length. Record the length.
  1. How long does it take for any surface point on the globe to travel in one complete rotation?

  2. Find the linear speed of any point that lies on the equator. To determine this value, use this equation: speed = distance/time. For example: the circumference of the Earth at the equator measures 24,900 miles. Divide 24,900 by 24 (time). The linear speed for this latitude is 1,037 mph. Compare that speed with the linear speed for a latitude that measures 12,000 miles around the globe (500 mph).

  3. Find the linear speed for any point that lies on the latitude of your city (follow Step 2). What's the difference in linear speed between your latitude and the equator?

  4. Which point has a greater linear speed? In which direction is this speed applied?

  5. Imagine an ocean current that continually veers to the right. What pattern will be formed by this motion?
  1. 24 hours
  2. 1,037 miles per hour
  3. answers will vary
  4. the point on the equator has the greater linear speed; to the right
  5. a clockwise circulation pattern
  1. Suppose an object traveling on a point due north from the equator maintains its linear speed. How will its extra linear speed affect its path?

  2. Will the motion of objects and currents in the Southern Hemisphere behave the same as in the Northern Hemisphere? Explain.
  1. It will cause the object to veer to the right. As it moves northward, its speed to the right becomes increasingly greater than the speed of the spinning Earth below, causing it to veer to the right.

  2. No. They will have a tendency to move to the left, forming a counterclockwise pattern.

Examine a spinning phonograph record (if you can still find one!). Discuss how the linear speed varies from the rim of the disc to the center of the disc. How might this example be used to teach about current movements?

One of the global consequences of changing ocean currents is the El Nino current. How do the Gulf Stream and El Nino affect your climate and weather?

After the Isthmus of Panama formed, animals traveling south did better than animals that went north. In fact, only three species from the southern continent survive in North America today. Why do you think this happened?


Four million years may seem like a long time, but in geological terms, it is relatively recent. This timeline should help put the timing of the formation of the Isthmus of Panama in perspective. You might elaborate on selected events in this abbreviated timeline. For example, make a timeline for the emergence and death of the dinosaurs. Or, make a timeline that includes various historic events on Earth, such as continental drift and the various changes in land masses over the millennia, like Pangaea and Gondwanaland.

Another challenging activity is to figure out how to demonstrate the passage of time using a scale that begins in your classroom and ends somewhere outside you school.

Note: this timeline is not to scale.


Scientific American Frontiers
Fall 1990 to Spring 2000
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now a part of Verizon Communications Inc.