Since Darwin's time, scientists have speculated the planet might be expanding or contracting. Even with the acceptance of plate tectonics half a century ago, which explained the large-scale motions of Earth's outermost shell, the accusations persisted; some Earth and space scientists continued to speculate on Earth's possible expansion or contractionon various scientific grounds.
"Our study provides an independent confirmation that the solid Earth is not getting larger at present, within current measurement uncertainties," said Xiaoping Wu of NASA's Jet Propulsion Laboratory.
Using a cadre of space measurement tools and a new data calculation technique, a team of NASA scientists detected no statistically significant expansion of the solid Earth. However, they did estimate the planet's radius changes, on average, by about 0.004 inches (0.1 millimeters) per year, or about the thickness of a human hair — a rate considered statistically insignificant. The newly established parameter will provide a basic framework against which scientists can measure the movements of Earth's crust; even though the planet isn't growing, it is constantly changing.
Tectonic forces such as earthquakes and volcanoes push mountains higher, while erosion and landslides wear them down. In addition, large-scale climate events such as El Niño and La Niña redistribute vast water masses among Earth's ocean, atmosphere and land. With the new baseline measure of Earth's actual size, scientists will be able to better understand the scale of these changes.
The team applied a new data calculation technique to estimate the rate of change in the solid Earth's average radius over time, taking into account the effects of other geophysical processes.
Geodetic techniques (satellite laser ranging, very long baseline interferometry and GPS) were used to obtain data on Earth surface movements from a global network of carefully selected sites. These data were then combined with measurements of Earth's gravity from NASA's Gravity Recovery and Climate Experiment (GRACE) spacecraft and models of ocean bottom pressure, which help scientists interpret gravity change data over the ocean. (OurAmazingPlanet)
Expanding Earth or Growing Earth is a hypothesis asserting that the position and relative movement of continents is at least partially due to the volume of the Earth increasing. While suggested historically, since the recognition of plate tectonics in the 1970s, the scientific consensus has rejected any expansion of the Earth.
Generally, the scientific community finds no evidence to support the expansion of the Earth theory, and uses the following arguments to dismiss it:
- Measurements with modern high-precision geodetic techniques show that the Earth is not currently increasing in size to within a measurement accuracy of 0.2 mm·y−1. Furthermore, the motions of tectonic plates and subduction zones measured by a large range of geological, geodetic and geophysical techniques supports plate tectonics.
- Mass accretion on a scale required to change the Earth's radius is contradicted by the current accretion rate of the Earth, and by the Earth's average internal temperature: any accretion releases a lot of energy, which would warm the planet's interior. Expanding Earth models based on thermal expansion contradict most modern principles from rheology, and fail to provide an acceptable explanation for the proposed melting and phase transitions.
- Paleomagnetic data has been used to calculate that the radius of the Earth 400 million years ago was 102 ± 2.8% of today's radius.
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