Nobody was around to observe the earth’s formation around 4.5 billion years ago, so the best we can hope for is to observe the state of the world today to learn how our home came. An essential part of that process is to find out if the inner core of the earth is a solid mass or some kind of shifting superheat slurry. Researchers from the Australian National University (ANU) believe that they have determined that the core of the earth is likely to be solid but a bit strange.
The key was to detect so-called “shear waves” derived from the nucleus. These are seismic waves that only propagate through solid rock, but the waves of the core are so small that nobody has been able to detect them yet. It was not even clear that there were some waves to discover. This is important because a liquid core could not transfer shear waves. A solid core would. If you can prove that shear waves spread through the nucleus, you have probably shown that it is solid.
Lecturer Hrvoje Tkalčić and Ph.D. Scholar Than-Son Phạm from ANU designed a method that meant waiting for an earthquake. A big one. The researchers call their method of measuring the core of the earth in the “wave field method”. After an earthquake, the sensitive seismic probes were used to record each little ass. But they can not start immediately after the earthquake. It takes about three hours for large rumbling to settle, which allows seismograms to record more subtle signals bouncing inside the ground. This is similar to many techniques used to measure the thickness of the Antarctic ice.
The study shows that seismic maps produced in this three to 10 hours after the earthquake window can essentially fingerprint the planet. The map shows the presence of shear waves coming from the planet’s core, and further allowing Tkalčić and Phạm to derive the velocity of the waves.
From these data, the researchers believe that they have determined that the kernel is solid. However, it is not a monolithic, unmoving lump. The core has elastic properties similar to gold and platinum. We still do not know the exact temperature of the core, its age or how fast it solidifies. The new waveform method could make it possible to get to know these things in the future.
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