How do we know what is at the centre of the Earth?

The world around us is full of mysteries, and one of the most intriguing is what lies deep within our planet. Despite the challenges of directly probing the vast depths, scientists have developed methods to unravel the structure of the Earth’s interior.

Volcanic eruptions provide valuable insights into the Earth’s internal dynamics. The glowing gases and molten rock that erupt to the surface reveal that extreme temperatures exist deep within.

But the most important tool for studying the Earth’s interior is the seismic waves generated by earthquakes. These waves vary in speed and direction as they pass through different layers of the Earth. By interpreting these variations using seismographs, scientists can deduce the structure and composition of the planet’s different layers.

How do we know what is at the centre of the Earth?
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Through such studies, we’ve come to understand that the Earth has a multi-layered structure. The uppermost layer, the crust, is up to 48 kilometres thick and consists of solid rock. Below this, to a depth of 2880 km, is the mantle, also made of solid rock. At the centre is the Earth’s core, with an outer liquid part filled with molten iron and nickel, and an inner solid core about 2560 km in diameter.

History of core hypotheses

The first hypotheses about the existence of the core were based on calculations of the Earth’s density and measurements of gravity. In the early 20th century, the work of scientists such as Richard Oldham and Benjamin Gershon confirmed the presence of a distinct core through seismic studies. Oldham first introduced the idea of a core using seismic wave analysis, while Gershon significantly advanced our understanding of its characteristics and formation.

The solid core and its influence on magnetism

Separated from the mantle by a liquid core, the Earth’s solid inner core was once thought to rotate independently, slightly faster than the Earth itself. However, recent discoveries by Chinese scientists suggest that the inner core has almost stopped rotating relative to the planet and may even be starting to rotate in the opposite direction. Such observations correlate with shifts in the Earth’s magnetic field and changes in the length of the day, shaving off fractions of a millisecond and revealing the dynamic interplay between the Earth’s layers. This differential rotation of the inner core is critical in generating the Earth’s magnetic field, which drives the geodynamo process.

Geomagnetic reversals and recent studies

Geomagnetic reversals, when the Earth’s magnetic poles change position, occur periodically. The last one occurred about 780,000 years ago. Recent findings by Chinese researchers may shed light on the mechanisms behind these reversals and their relationship to the rotation of the solid core. A weakened magnetic field during a polarity reversal could increase the Earth’s vulnerability to solar radiation, potentially affecting technology and life forms that depend on the magnetic field.

The scientific community is divided over the Chinese scientists’ findings. Despite the frenzy in the media, a significant number of experts argue that the data needs more scrutiny. It’s possible that their results could be interpreted differently. Nevertheless, exploring the inner structure of the Earth and its magnetic field remains crucial to understanding the geological and ecological complexities of our planet.

Prepared by Christina Ashmole

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