Monday, October 4, 2010

The Earth is Slowing...

The Earth's rotation is the rotation of our planet around its own axis. At present, the angular speed of Earth's rotation in inertial space is 7.2921150 ± 0.0000001 × 10−5 radians per SI second (mean solar second). Multiplying the value in rad/s by Earth's equatorial radius of 6,378,137 m (WGS84 ellipsoid) (factors of 2π radians needed by both cancel) yields an equatorial speed of 465.1 m/s or 1,674.4 km/h.

But is the Earth's rotation slowing down? In short, yes, due to a transfer of Earth's rotational momentum to the Moon's orbital momentum as tidal friction. And with that increase in the Moon's speed, it is also causing the Moon to slowly recede from Earth. The slowing rotation of the Earth results in a longer day and also a longer month. Once the length of a day equals the length of a month, the tidal friction mechanism will stop. But not only is the Earth losing it's kinetic energy to tidal friction, but also other forms of friction.

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. 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.

Does this spell a slow but inevitable doom for our planet, or are there more imminent threats to our survival? In any case, we are on this Earth but only just a moment, and will be gone just as quick.


Arthur N. Cox, ed., Allen's Astrophysical Quantities p.244.