Formerly, there were only four layers of Earth: the crust, mantle, liquid outer core and solid inner core. Now, scientists have revealed a new, distinct layer within our planet’s inner core, which could help inform the evolution of Earth’s magnetic field.
In a new study released this month, a pair of seismologists at the Australian National University documented new evidence of a 400-mile thick solid metallic ball at the center of Earth’s inner core – like the smallest figurine of a massive, planetary Russian nesting doll set. The new layer consists of an iron-nickel alloy, like other parts of the core. But it has a different crystal structure that causes shock waves from earthquakes to reverberate through the layer at different speeds than the surrounding core, the study found.
Researchers study the inner core to better understand Earth’s magnetic field, which protects us from harmful radiation in space and helps make life possible on our home planet. Geophysicists surmise the inner core could have formed less than a billion years ago, which is relatively young on a geologic time scale. The study authors explain the inner core grows outward by solidifying materials from the liquid outer core, releasing heat and creating convection currents. This convection generates Earth’s magnetic field.
The inner core, which was discovered in 1936 by Danish seismologist Inge Lehmann, makes up less than 1 percent of Earth’s volume (Earth’s center is located about 4,000 miles below the surface). Its distance beneath the surface and small size, though, make it difficult for scientists to measure by direct measurements, so instead they study shock waves triggered by earthquakes.
When a large earthquake strikes, the resulting shock waves, or seismic waves, can bounce back and forth from one side of the Earth to the other like a ping-pong ball, said Pham. Seismic waves travel at different speeds through Earth’s different layers depending on its density, temperature and composition. Like a radiologist studying a patient’s internal organs, scientists use instruments known as seismometers around the world to measure these oscillations and learn about the inner workings of our Earth.
Twenty years ago, researchers used seismograph data and proposed the existence of a fifth layer. Since then, Pham said the evidence of the innermost inner core “has become strengthened with time with more and more data.” But his new study takes it further, analyzing unprecedented seismograph data.