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Science British researchers find direct evidence of solid inner core of Earth
Science British researchers find direct evidence of solid inner core of Earth | British researchers find direct evidence of solid inner core of Earth |
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| by William Atkins | |
| Monday, 18 August 2008 | |
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Page 2 of 2 Their abstract, thus, states, “We present two observations of an inner-core shear-wave phase at higher frequencies in stacked data from the Japanese High-Sensitivity Array, Hi-Net. From an analysis of timing, amplitude and waveform of the 'PKJKP' phase we derive constraints on inner-core compressional-wave velocity and shear attenuation at about 0.3 Hz which differ from standard isotropic core models.” According to the Wednesday, August 13, 2008 Science News article (subscription required) “Firm evidence that Earth’s core is solid,” “Some types of ground motions triggered by earthquakes — in particular, those that travel like sound waves — can pass either through solid rock or through a liquid such as water or molten iron.” Most importantly (underlined for emphasis), as reported by Science News: “But the size, shape and timing of some of the vibrations picked up by the Japanese instruments suggest that the waves traveled through the planet’s inner core as shear waves, which can travel only through a solid material ....” Fortunately, the Wookey-Helffrich team obtained high-frequency vibrations and a large network of seismometers. Science News reports on their methods of analysis, “Many of the seismometers had been installed in boreholes more than one kilometer below Earth’s surface — a depth that insulated the sensors from noise generated by human activity and that also made the faint ground motions easier to discern.” Helffrich reports in the article, “It took heroic measures to detect these signals.” Science News reports, “… the characteristics of the ground motions the team noted after the African quake were consistent over a broad area, a sign that local geological variations probably didn’t create spurious reflections that could have confused the analysis….” The team’s conclusions, as reported by Science News, was, “The ground vibrations triggered by the core-crossing shear waves were larger than those estimated by current seismic models, a sign that the solid material in the inner core attenuated the waves much less than expected…. That, in turn, could mean that the solid material of the inner core doesn’t include many vibration-dampening pockets of melted material, as some scientists have proposed.” [Author's note: The work of the Wookey-Helffrich team is helping to better understand the nature of Earth's center. Their work is providing more accurate measurements of the Earth's center, along with additional data on the structure of the Earth. Even today, other scientists are conducting studies that are showing the Earth may likely still contain an "innermost" inner core that first formed over 4.5 million years ago--when the Earth first began to take shape. Such work to study this innermost inner core may very well help us learm more about Earth's earliest formation within the solar system.]
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