Today, we’re diving into one of the most unusual scientific discoveries about our planet - a mysterious gravitational anomaly that reveals something extraordinary happening thousands of kilometers beneath the Earth’s surface.

This discovery wasn’t found through digging or drilling. It was found thanks to NASA’s incredible satellite mission known as GRACE (Gravity Recovery and Climate Experiment). This accidental finding challenges our understanding of how fast the deep Earth can change and hints at a profound connection between the planet’s mantle and its magnetic field.

Key Takeaways from this Discovery:
  • Earth's gravity is not uniform; it varies based on the density of the material below.
  • In 2007, NASA's GRACE satellites detected a massive, unexplained gravity shift near Africa.
  • The anomaly was traced to a rapid change in mineral density nearly 3,000 km below the surface, near the core-mantle boundary.
  • This suggests that deep Earth processes can happen in years, not just millions of years.
  • The event coincided with a "geomagnetic jerk," hinting at a link between the mantle and Earth's magnetic field.

🛰️ How We Weigh the Earth from Space

To understand this discovery, we first need to know how gravity mapping works. Earth’s gravity varies slightly depending on the density of the materials beneath your feet.

To measure these tiny differences, NASA launched the GRACE mission, which consisted of two identical satellites orbiting Earth in perfect tandem. A hyper-precise laser system between them measured the distance down to the micron.

The principle is simple but brilliant:

  • When the lead satellite passes over an area with stronger gravity (like a dense mountain range), it accelerates slightly, increasing the distance to the trailing satellite.
  • When it passes over an area with weaker gravity, it slows down, decreasing the distance.

By tracking these minute changes, scientists can create a stunningly detailed map of Earth’s gravitational field.

A clean infographic diagram of the GRACE satellites orbiting Earth, showing how their distance changes over gravity anomalies.

🌀 The 2007 Gravity Mystery

Something truly bizarre happened between 2006 and 2008. While analyzing GRACE data, scientists discovered a massive, unexplained gravity anomaly that peaked in January 2007.

This event covered over 7,000 km across the eastern Atlantic Ocean, near Africa. The signal was far too large and too strong to be explained by normal surface events like water movement or air pressure. This led scientists to look deep below the crust, into Earth’s mantle.

🔥 The Deep Earth Hypothesis: A Phase Change at the Core

The best explanation for this enormous gravity shift lies roughly 3,000 km below the surface, at the boundary between the molten outer core and the solid mantle.

Scientists believe the event was caused by a rapid mineral phase transition.

  • The deep mantle is composed of a mineral called bridgmanite.
  • Under the immense pressure and heat, a huge plume of this material likely shifted.
  • This shift caused the bridgmanite's crystal structure to change into a denser phase, similar to how water freezes into denser ice (though in this case, it became more dense).

Essentially, a continent-sized chunk of Earth’s deep interior changed its state, causing a massive redistribution of mass that was detectable all the way up in space.

A dramatic cross-section of the Earth's interior, showing the crust, mantle, and core, with a glowing anomaly near the core-mantle boundary beneath Africa.

This event occurred near a mysterious deep-Earth structure known as the African Large Low Shear Velocity Province (LLSVP) - a massive blob-like formation thought to influence volcanic and tectonic activity. The 2007 shift may have altered this structure, suggesting that these deep processes can change much faster than we ever imagined.

A Magnetic Coincidence?

Even more intriguingly, the same time period saw a sudden global geomagnetic jerk - a rapid change in the flow of Earth’s magnetic field.

This coincidence hints that deep mantle processes (like the gravity anomaly) may directly influence the motion of the molten iron core, which generates Earth’s magnetic field. If true, it means what happens thousands of kilometers beneath us could affect everything from our planet’s magnetism to long-term climate patterns.

🧠 What This Means for Science

This 2007 event is a groundbreaking discovery because it challenges our long-held assumptions about the “slow and steady” nature of geology.

It suggests that:

  1. The deep mantle can change on a human timescale (years), not just a geological one (millions of years).
  2. Events at the core-mantle boundary can have detectable effects on the surface, influencing both gravity and magnetism.
  3. Our planet is far more dynamic and interconnected than previously thought.

It’s a powerful reminder that Earth is not a static rock, but a living, breathing, and ever-shifting world.

Study Reference: Charlotte Guran et al. - Deep Mantle Mass Redistribution Detected by GRACE