In March 2011, a 9.0 magnitude earthquake struck the east coast of Japan. This earthquake, in addition to the great destruction and tsunami it created, shifted the Earth’s axis and shortened the days on Earth.
The strongest recorded earthquake to hit the country shifted the planet’s axis by about 17 centimeters and may have shifted the main island by about 2.4 meters. Like other similar large earthquakes, it changed the rate of Earth’s rotation.
From NASA’s Jet Propulsion Laboratory, Dr. As Richard Gross explained to Popular Mechanics in 2011, “Earthquakes can change the Earth’s rotation by rearranging the Earth’s mass. That’s what a spinning figure skater does to make him spin faster. By bringing his arms close to his body, he brings his mass closer to the axis around which it rotates. And earthquakes do the same. This earthquake must have brought the mass, on average, a little closer to the Earth’s axis of rotation, causing the Earth to spin faster and the length of the day to be slightly shorter.”
Gross studied how the mass distribution changed by looking at models of the Earth’s mass distribution prior to the earthquake and using estimates of how the fault shifted during the earthquake: “Then, through conservation of angular momentum, if I know how the Earth’s mass is rearranged, how does the Earth’s rotation change? I know too.”
The earthquake appears to have accelerated the Earth’s rotation by about 1.8 microseconds. The Indonesian earthquake in 2004 also accelerated Earth’s day by an estimated 2.68 microseconds.
However, earthquakes are not the only events and factors that affect the rate of Earth’s rotation. From NASA’s Goddard Space Flight Center, Dr. Benjamin Fong Chao said after the 2004 Indonesia earthquake, “Any earthly event involving the movement of mass affects the Earth’s rotation, from seasonal weather to driving a car.”
There are many different factors that affect the rate of rotation, such as changing sea levels and shifts on Earth, but the biggest factor is the Moon’s distance from Earth. As the two space bodies interact, the Earth slows down as a result, although occasional bursts of velocity occur during the Moon’s retraction.
- The Moon is moving away from Earth, albeit slowly. So what does this event called “The Lunar Withdrawal” mean for Earth and humanity?
By looking at ancient corals, scientists determined that the Earth rotated much faster 444 to 419 million years ago. As the coral grows each day, it leaves a thin layer of calcium. Because corals grow more in the dry season than in the wet season, you can count the calcium carbonate deposits in each season and calculate how many days pass in a year, similar to tree rings. Using this method, the team calculated that Earth lived 420 days a year between 444 and 419 million years ago, before slowing down under the influence of our Moon.
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