Earth's Slowing Rotation

"The Earth's Slowing Rotation!" Its Geophysical Effects!

Donald L. Hamilton

It is a known fact that the rotation of the Earth is gradually slowing. For four and one half billion years, its entire life, it has been slowing down. As the Earth loses its kinetic energy due to all forms of friction acting on it (tides, galactic space dust, etc.) like any other flywheel, it will slow down. From time to time our timekeepers must adjust their super accurate atomic clocks to synchronize them with the Earth's slowing rotation whose day/night cycles we base our lives on.

Scientists estimate that the Earth's rotation is slowing at the rate of 2.2 seconds every 100,000 years. The time it takes the Earth to complete one rotation increases 2.2 seconds every 100,000 years. This is a very conservative figure considering the number of adjustments our timekeepers have been forced to make in recent years. If we trace this phenomenon back in time, whatever the correct figure is, at one point in time it may have taken the Earth 12 hours to complete one rotation, (depending on its initial speed of rotation when it was created.) At that time the Earth was spinning at twice the speed it is traveling at the present time.

The constant gravitational force and the weakening angular momentum caused by the slowing of the Earth's rotation has had a profound effect on the Earth's geophysical activity throughout the ages. Throughout the life of the Earth there has been a continual adjusting of the Earth's shape as the ratio of the strengths of angular momentum and gravity has changed. Gravity is a centripetal force, it exerts its tremendous force inward, toward the center of gravity, always trying to form the Earth into a perfect sphere.

The angular momentum of spinning planet tends to adjust the bulge to fit the changing conditions. A stronger angular momentum due to a faster rotation would increase the bulge while a weaker angular momentum due to a slowing rotation would allow gravity to form into a more perfect sphere. The rotation is constanly slowing however so the the angular momentum is always growing weaker. (The bulge does not decrease enough to increase the rotation of the Earth by any significant amount.)

This allows gravity to pull the planet's shape into an evermore perfect sphere. This action has caused a continual change in the planet's shape to occur. This change in shape has set up tremendous stresses within the Earth and in its crust as it struggles to fit on the slowly changing mantle.

In the past, when the Earth was younger and spinning faster, the stronger angular momentum caused the Earth to assume a more pronounced oblate spheroid shape. (At the present time the planet Saturn is spinning much faster then the Earth and displays this more pronounced oblate spheroid shape.) When the Earth was spinning faster the bulge was much greater then the twenty-seven miles it is today. A 5% increase in the equatorial circumference of the Earth would produce approximately 1200 more miles of surface around the equatorial zone.

If the Earth's rotation was not slowing, there would be none of this stress, and its shape would have remained constant throughout the ages. Its rotation is gradually slowing however, (even taking the conservation of momentum into consideration), causing its angular momentum to become progressively weaker. Gravity remains just as strong as ever and continues to exert the same amount of pressure.

This on going change causes tremendous dynamic movement within the Earth as it adjusts its shape. It is gradually changing its shape from that of an oblate spheroid with a bulging equator and flatter pole regions to that of a more perfect sphere to conform with the changing conditions. Throughout the ages, since its birth, the Earth has been going through this constant gradual change.

The surface of the Earth's mantle, especially in the tropical and subtropical regions of the Earth is becoming smaller while the pole regions have uplifted and become rounder. The fact that the Earth is getting rounder, even today, has been confirmed by the satellite "Lageos" which is being monitored by scientists at the University of Texas Center for Space Research and at the Jet Propulsion Laboratory.

This slow continual change of the Earth's interior has set up tremendous dynamic pressures and stress within the Earth's crust as it endeavors to conform to the ever changing mantle upon which it floats. It is the imbalance between the rotational inertia and gravity that cause the dynamic movements of the continental crustal plates as the crusts shifts and crunches to fit into the ever changing area.

It is this constant change thats causes earthquakes to occur, volcanoes to erupt and the Earth's vast mountain ranges to rise. As the equatorial oblate shape of the Earth shrinks, the immense resulting pressure within the mantle causes it to gradually ooze upward creating the Atlantic and Pacific ridges.

The Earth's slowing rotation also had a profound effect on its climate over the ages. In the past, the stronger angular momentum caused the Earth's ocean waters to concentrate more in the tropical and subtropical regions. The Earth's tidal bulges, due to this concentration, were greater also. This left the oceans in the pole regions very shallow. Even today the Arctic Ocean's average depth is more shallow then the oceans in the equatorial regions. Also the continent of Antarctica's plateau has greater average height above sea level then the other continents, even though burdened with heavy glaciers.

This is probably due to the lower sea level in the pole regions rather then a higher continent. The concentration of ocean water over a much larger area, due to its more oblate shape in the warmer regions of the Earth, must have had a profound effect on the Earth's climate in past geological times.

The faster rotation also had an enormous effect on the Earth's dynamic atmosphere creating more energetic global winds and perhaps, greater evaporation. The blanket of atmosphere may also have been thicker in the equatorial regions. The final result of all these effects created a vastly different climate then our present climate. These effects where greatest in the Pre-Cambrian age of geological time. They have become more subdued, but still evident, in the later geological ages as our planet's rotation continues to gradually slow.

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