Thursday, July 12, 2007

Earth Is Smaller Than Thought, New Measurements Show

Earth Is Smaller Than Thought, New Measurements Show
Kate Ravilious
for National Geographic News
July 9, 2007

New measurements reveal that Earth is smaller than was previously thought—though not by much.

If you're a planning a trip around the world, you may be pleased to hear that you have about 0.1 inch (2.5 millimeters) fewer to travel.

Although the change is tiny, experts say it could have implications for predicting sea-level rise and the effects of global warming (get the facts on global warming).

Using a suite of sophisticated techniques, a team of international scientists has spent the last two years measuring nooks and crannies all over Earth, noting how they have changed and comparing the new measurements with those taken in 2002.

In addition to revealing Earth's slightly slimmer silhouette, the results reveal that the Pacific seafloor is the most restless place on the planet, traveling to the northwest by around two inches (five centimeters) a year.

Meanwhile, much of Scandinavia and northern Canada are bobbing up in elevation some 0.2 to 0.3 inch (5 to 8 millimeters) a year, and North America is pulling apart from Europe at a rate of around 0.7 inch (18 millimeters) a year.

The changes do not indicate that Earth is shrinking but rather that previous estimates—measured from Earth's core to its surface—were slightly off, the researchers explained.

"Earth's physical shape hasn't changed since last time, but we have just shown that on average our 400 observation sites lie around 2.5 millimeters closer to the center of the Earth," said Axel Nothnagel, a mathematician at Germany's University of Bonn who took part in the research.

A Mammoth Calculation

One of the techniques used to measure these planetary jiggles involved more than 70 radio telescopes situated all over the world, each picking up radio waves from quasars—young galaxies billions of light-years away.

"Because quasars are so far away, they appear stationary and so they are an ideal fixed point in the sky," Nothnagel explained.

In the same way that early sailors used stars to navigate, Nothnagel and his colleagues used the quasars' signals to calculate how far various spots on Earth have moved from each other.

Another technique used in the study measured the distance between Earth and various satellites in the sky.

Overall the study used 400 observation sites and compiled data taken between 1984 and 2005. Analyzing all the data and carrying out the calculations took two years.

So why do these tiny movements matter, and do we really need to know Earth's size to the nearest millimeter? The answer is probably yes, if you live on a sinking continent.

"[The measurement] provides us with access to a coordination system against which we can measure environmental change," said Marek Ziebart, a mathematician at University College London who wasn't involved in the study.

If ice caps continue to melt or water begins to evaporate from the Amazon Basin, these new exact measurements will enable scientists to more accurately track the effects, Ziebart explained.

(See an interactive map of the effects of global warming.)

"If you have a tide gauge telling you that the sea level is rising, how do you know that it is not the continent which is subsiding [or sinking]?" Nothnagel said.

For scientists who want to determine whether the sea level has risen by just a millimeter a year, the measurements on the ground have to be just as precise, he said.

The new measurements also allow scientists to monitor continuing trends that have been spotted in previous surveys, the research team noted.

North America and Europe continue their steady parting of ways, as the Atlantic Ocean grows wider due to the process of continental drift.

Meanwhile, northernmost sections of Europe and North America keep gaining in elevation, as they buoy up after the huge weight of ice was lifted at the end of the last ice age.

"Canada and Scandinavia are responding to post-glacial rebound," Nothnagel said.

He and his colleagues are now gathering data for the next mammoth calculation effort, which is due to begin in 2008.

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