Back in 1978, moviegoers were treated to an amazing sight: Superman reversing the spin of the Earth, turning back time in the process (and saving his beloved Lois). Preposterous, of course, but what if something did change the Earth's rotation? What if the rotation stopped completely?
Let's get our admittedly far-fetched assumptions on the table. First, let's assume the Earth stopped spinning gradually, as a sudden deceleration would mean disaster. Second, we'll suppose that Earth's ecosystems have survived the transition mostly intact. So what does this new world look like?
For starters, Earth would now take a whole year to do what it pulls off in a day: cycle from night to day and back. Cities would spend half the year in darkness and half the year in full sunlight, just like the North and South Poles do today. And, like the poles, every region would still experience different seasons, but the temperature swings from season to season would be much greater for areas along the equator. An equatorial region would spend infernally hot months very close to the sun, while that area's global counterpart would spend dark, frigid months very far away from it. That's trouble for the plants and animals that have adapted to the climate of a region and, consequently, for the people living there as well.
What's that? You're relocating to the relatively stable (though still awfully cold) polar regions? Bad move. They're deep underwater. In fact, the boundaries between ocean and land on a spin-free Earth would look nothing like they do today. Because the Earth rotates, centrifugal force causes the planet to bulge along the equator. No rotation, no bulge. Without that bulge, all of the extra water held in place along the equator would go rushing back toward the poles. Esri, a company that develops geography-focused technology, modeled the world's land and oceans after its equatorial bulge subsided and found that the Earth would have a band of land -- one giant supercontinent -- that circles the equator and separates two massive oceans to the north and the south.
As if that weren't enough, Earth's magnetic field might go away, too. While we're not entirely sure how that magnetic field is generated, one leading theory states that it's the result of Earth's inner core rotating slightly faster than outer core (yep, two different rotations on one planet). If both of them stop, the mechanism behind Earth's magnetic field may as well, leaving us exposed to potential harmful solar winds [source: Cain].
Where does that leave us? Humans are an adapatable species with powerful technology at their disposal, but survival in this new environment would be a challenge. Sure, we could try to light our homes in the darkness and heat and cool them (at great cost) during wild temperature swings, but not everything would be under our control. Could crops survive the extremes of this new world? Could any plants? If not, the entire food chain would be in danger. Perhaps we could find new crops or modify existing ones to tolerate this new environment. Or maybe we would become dependent on perennials that return with warm weather. It's actually a little comforting to think that, while the world will probably become a hellish place to live, at least our decorative hosta beds might be OK.
Why Does Earth Spin?
You have to admit, it doesn't feel like you're spinning around the center of the Earth at hundreds of miles an hour, so it's not hard to cut our scientific forebears some slack for assuming the Earth was stationary and that the sun rotated around it. Thankfully, Copernicus set the record straight with his heliocentric model, and we now know that the Earth spins on its axis as it revolves around the sun. But why does our planet spin in the first place?
Remember Newton's first law of motion? It states that an object remains in whatever state of motion it's in unless another force acts upon it. The Earth is rotating because it's been doing that as long as it has existed.
Before there were planets in our solar system, there was a spinning, nebulous cloud of dust with our sun at the center. Over time, these dust particles collided into one another and began to stick, forming larger and larger rocks and ultimately planets through a process known as accretion. But remember, the cloud of dust -- or accretion disc -- was rotating from the start. As the particles that formed the Earth began to stick together, that momentum was conserved, causing the growing planet to spin faster and faster, much the way a figure skater does when he pulls his arms in toward his body. By the time the Earth had formed, it had all of the angular momentum it would need to keep spinning to this very day. Just how fast is that anyway?
How Fast Does Earth Spin?
As any police officer can tell you, measuring the straight line speed of a car -- or most any object -- is a fairly simple and reliable process. Measuring the speed of a rotating object like the Earth is slightly more complicated. After all, if you stand at one of the poles, you'll spin right along with the rest of the Earth, but you'll be stationary with respect to its center. Stand on the equator, though, and you'll have a linear speed of 1,036 miles per hour (1,667 kilometers per hour) [source: Esri]. That's faster than the speed of sound, and one of the reasons we tend to launch rockets toward the east [source: NASA]!
The difference between linear speed at the poles and at the equator produces an interesting phenomenon called the Coriolis effect. The effect is easiest to visualize if you think about someone setting out in a plane straight for the North Pole from the equator. Since the plane retains the lateral speed of the equator, it appears to curve with respect to the Earth as it approaches the slower moving poles.
Is there anything slowing the Earth's rotation down? Sure, but don't adjust your watches just yet. The forces changing the speed of the Earth's rotation make an extremely small impact. The tides, which are caused by the gravitational forces between the Earth, the sun and the moon, produce tidal friction as they interact with the Earth. That drag adds about 2.3 milliseconds to our day every century [sources: Lunar and Planetary Institute, Ray]. Weather systems can change the Earth's rotation, with winds applying a braking force to the planet's surface. Finally, earthquakes can mess with the length of the day by actually redistributing the Earth's mass. The 2011 earthquake that struck Japan actually accelerated the Earth's spin (because it shifted the mass toward the equator) and shortened the day by 1.8 microseconds [source: CBS News].
So, the next time you complain about the day being too long or too short, don't despair: It's changing all the time.
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More Great Links
- Cain, Fraser. "Solar Wind." Sept. 17, 2008. (Feb. 11, 2012) http://www.universetoday.com/18269/solar-wind/
- CBS News. "Earth's day length shortened by Japan earthquake." March 13, 2011. (Feb. 11, 2012) http://www.cbsnews.com/stories/2011/03/13/scitech/main20042590.shtml
- Coffey, Jerry. "Why does the Earth rotate?" May 23, 2008. (Feb. 11, 2012) http://www.universetoday.com/14491/why-does-the-earth-rotate/
- Ćuk, Matija. "Planetary science: Kick for the cosmic clockwork." Dec. 22, 2011. (Feb. 11, 2012) http://www.nature.com/ngeo/journal/v5/n1/full/ngeo1362.html
- Fraczek, Witold. "If the Earth Stood Still." Esri. (Feb. 11, 2012) http://www.esri.com/news/arcuser/0610/nospin.html
- Iowa State University. "Earth's Rotation." 2001. (Feb. 11, 2012) http://www.polaris.iastate.edu/NorthStar/Unit3/unit3_sub1.htm
- Jessa, Tega. "Why are There Seasons?" Universe Today. Oct. 15, 2010. (Feb. 11, 2012) http://www.universetoday.com/75843/why-are-there-seasons/
- NASA. "Changes in the Earth's Rotation are in the wind." March 4, 2003. (Feb. 11, 2012) http://earthobservatory.nasa.gov/Newsroom/view.php?id=23097
- Natural History Museum. "How did the solar system form?" (Feb. 11, 2012) http://www.nhm.ac.uk/nature-online/space/planets-solar-system/formation/index.html
- Nave, R. "Angular Momentum." Georgia State University. (Feb. 11, 2012) http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html
- Lunar and Planetary Institute. "Sky Tellers - About Day and Night." Jan. 4, 2007. (Feb. 11, 2012) http://www.lpi.usra.edu/education/skytellers/day_night/about.shtml
- Office of Naval Research. "Observing the Sky: Motion of the Earth - Rotation." (Feb. 11, 2012) http://www.onr.navy.mil/focus/spacesciences/observingsky/motion1.htm
- Pandian, Jagadheep D. "Why do planets rotate?" Cornell University. Oct. 18, 2005. (Feb. 11, 2012) http://curious.astro.cornell.edu/question.php?number=416
- Ray, Richard. "Ocean Tides and the Earth's Rotation." May 15, 2001. (Feb. 11, 2012) http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html
- Shelton, Mike. "Probing Question: Why does the Earth rotate?" Aug. 6, 2007. (Feb. 11, 2012) http://www.physorg.com/news105637304.html
- Simanek, Donald E. "Tidal Misconceptions." Lock Haven University. June 2011. (Feb. 11, 2012) http://www.lhup.edu/~dsimanek/scenario/tides.htm
- Springbob, Christopher. "What makes the Earth rotate?" Cornell University. October 2002. (Feb. 11, 2012) http://curious.astro.cornell.edu/question.php?number=329
- Stern, David P. "The Rotating Earth." NASA. Sept. 22, 2004. (Feb. 11, 2012) http://www-spof.gsfc.nasa.gov/stargaze/Srotfram1.htm
- University of Tennessee. "Consequences of Rotation for Weather." (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/earth/coriolis.html
- University of Tennessee. "Conservation of Angular Momentum." (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/solarsys/angmom.html
- University of Colorado. "How Planets Form." August 2007. (Feb. 11, 2012) http://lasp.colorado.edu/education/outerplanets/solsys_planets.php
- University of Tennessee. "Johannes Kepler: The Laws of Planetary Motion." (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/history/kepler.html
- University of Tennessee. "Newton's Three Laws of Motion." (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html
- University of Tennessee. "The Copernican Model: A Sun-Centered Solar System" (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/retrograde/copernican.html
- University of Tennessee. "The Earth's Magnetic Field." (Feb. 11, 2012) http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html
- U.S. Geological Survey. "Earth's spinning core provides magnetic protection and disaster movie material." Oct. 9, 2003. (Feb. 11, 2012) http://hvo.wr.usgs.gov/volcanowatch/2003/03_10_09.html