Identical 270-million-year-old fossil bands of an extinct reptile known as Mesosaurus had been found in eastern South America and in western Africa. Wegener concluded that this was only possible if South America and Africa had been joined at one time. Numerous other discoveries of corresponding fossil bands for extinct life-forms on different continents further supported this theory.
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Using Fossil Evidence to Calculate Continental Drift
The coal fields of southwestern Ohio are part of a long band of coal deposits that stretch down the eastern part of the United States. The Powhatan No. 6 Mine in Alledonia is one of the biggest coal mines in Ohio.
- Click here to see the location of this coal mine in southwestern Ohio.
Coal is formed primarily from plant remains found in swampy, tropical areas. The tropics are defined as the equatorial band that stretches in the north from the Tropic of Cancer at a latitude of 23°N to the Tropic of Capricorn in the south at a latitude of 23°S.
- Click here to add in the locations of the Tropic of Cancer and the Tropic of Capricorn.
- Use the measuring tool to determine the distance (in km) from the Powhatan No. 6 Mine in Ohio to the Tropic of Cancer and to the Tropic of Capricorn. Distance from the Powhatan No. 6 Mine to the Tropic of Cancer: approximately 1,800 km (1,120 miles). Distance from the Powhatan No. 6 Mine to the Tropic of Capricorn: approximately 7,000 km (4.350 miles). Note: Answers will vary slightly depending on exactly how the distance was measured.
The coal fields of southwestern Ohio are part of a rock formation that is estimated to be approximately 300 million years old.
- Calculate the speed (in cm/year) at which Ohio has drifted, if we assume that it has traveled the minimum distance from the Tropic of Cancer. Speed of Ohio if drifting from the Tropic of Cancer: 1800 × 105 cm / 300 × 106 years = 0.6 cm/year
- Calculate the speed (in cm/year) at which Ohio has drifted, if we assume that it has traveled the maximum distance from the Tropic of Capricorn. Speed of Ohio if drifting from the Tropic of Capricorn: 7000 × 105 cm / 300 × 106 years = 2.3 cm/year
- The current speed of the North American continent is estimated to be about 2.5 cm/year. How well do your answers compare with the current rate? My answers are slightly below the currently accepted rate of 2.5 cm/year.
- What assumption have you made about the direction that Ohio is traveling in your speed calculations? In my calculations, I assumed that Ohio had traveled directly north from the Tropics.
- How would your values have changed if you had assumed that Ohio also had some sideways drift as it moved from the Tropics? Could this explain the difference between your calculated speeds and the accepted value in question 4? The travel distance would have increased if Ohio had also had some sideways drift as it traveled from the Tropics. This increased distance would have resulted in an increase in my speed values in my calculations. This is probably one reason why my calculated values are below the currently accepted value.