MadSci Network: Earth Sciences

Re: Is continental drift caused by earth expansion?

Date: Thu May 7 10:04:03 1998
Posted By: Bill Raatz, Ph.D., Exploration geologist, Stratigraphy/sedimentology, ARCO International Oil & Gas Co.
Area of science: Earth Sciences
ID: 893966532.Es

Dear A. Compton,

Thanks for your interesting question on the idea of an expanding earth as the driving mechanism of continental drift. In short, almost no one subscribes to the expanding earth hypothesis. A very few free thinkers in Australia support the idea, and I think one professor at either the Univ. of Texas or Texas A&M.

As you rightly observe, on the surface the idea has some merit. A reconstruction based on a small earth composed entirely of land which then breaks apart due to expansion would fit our observations that continents were at one time all connected. There are some problems, however, and today almost all scientists believe that the earth has retained pretty much the same size through time and that land masses float atop a liquid mantle and move due to mantle convection.

I have not made a study of the small earth hypothesis, but the following general points against it come to mind:

  1. The earth, like all rocky planets, is cooling through time. Cooling creates contraction rather than expansion.

  2. A smaller earth implies that the earth either had less mass or was more dense in the past. If it had less mass, it could only gain more through meteor bombardment, which is quite a small source of material. If it was more dense, this implies that it was cooler which goes against point number 1.

  3. Modern measurement techniques are so sophisticated that I think if the earth were actually expanding we could detect it. It is true that the earth's shape subtly changes through time (the study of this is called geodesy) but the absolute volume does not change.

  4. The small earth hypothesis predicts that all of the continents were together at the earth's beginning (say 5 billion years ago), and as expansion occurs through time they drift further and further apart. Although the earth's land mass has been connected in the past, the timing of this supercontinent (called Pangea) is very precisely known from both fossil and magnetic evidence to be only about 250 million years ago. In fact, detailed reconstructions of plate movement through time shows that the early earth had lots of small microcontinents that randomly collided and accreted. This is why large continents have their oldest rocks in the center with successively younger rock outward. Landmasses have come together and broken apart many times in earth's history without following the predicted pattern of less interaction through time as supposed by the expanding earth model. What we see today as far as the earth's continents fitting together like a puzzle is simply the result of the latest break up. In the future, continents will again collide and break apart. India's collision with Asia forming the Himalayas is a present-day example.
Cranky feeling ideas that are contrary to present thinking are incredibly valuable both because they force us to reexamine our assumptions and because when true, they revolutionize our views of the earth. Therefore I wouldn1t pass absolute judgment against the idea, especially when I haven't investigated the subtleties of the expanding earth people's arguments. That being said it is very very unlikely to be true. I encourage you to investigate it further.

Bill Raatz

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