Earth's Giant Mantle Blobs Shift Shape Like Continents, New Models Show

Two continent-sized structures lurk nearly 1,800 miles beneath your feet, one anchored under Africa, the other under the Pacific Ocean. Geologists call them blobs—massive accumulations of rock in Earth's mantle, the thick layer of slowly flowing stone between the crust and the core. We know they exist because they slow down seismic waves from earthquakes, a telltale sign that they are hotter than the rock surrounding them. For decades, scientists have watched these formations with a mixture of fascination and uncertainty, knowing they were there but puzzled about how they had moved and changed across billions of years.

These blobs are not inert. They are thought to be the source regions for deep mantle plumes—towering columns of superheated rock that rise toward Earth's surface and trigger some of the planet's most violent volcanic eruptions. When these plumes breach the crust, the results can be catastrophic. The extinction event that killed the dinosaurs 65.5 million years ago was partly driven by volcanic activity linked to mantle plumes. The blobs also appear to control the movement of kimberlite, a type of rock that carries diamonds from depths of 120 to 150 kilometers, and sometimes from as far down as 800 kilometers, up to where humans can find them.

For a long time, the prevailing theory held that these blobs were essentially fixed in place—anchors locked into the mantle for hundreds of millions of years while tectonic plates shuffled around above them. But new research challenges that picture entirely. Using Australia's National Computational Infrastructure, a team of geologists ran advanced simulations modeling a billion years of mantle flow. What they found was striking: the blobs do not stay put. Instead, they shift position and reshape themselves in patterns strikingly similar to how continents assemble into supercontinents and then break apart.

The models work by reconstructing how tectonic plates have moved across Earth's surface over deep time. When plates collide, ocean floor gets pushed downward in a process called subduction. That cold, dense rock sinks deeper into the mantle, and once it reaches about 2,000 kilometers down, it physically shoves the hot blobs aside. Over geological time, this process causes the blobs to migrate, merge, and separate. The African blob and the Pacific blob can come together to form what the researchers call a "superblob," then drift apart again as plate movements shift.

One finding proved particularly surprising: the African blob assembled into its current configuration only about 60 million years ago—far more recently than earlier models suggested. Previous work had implied the blob might have held roughly its present shape for nearly ten times as long. This revision matters because it means the deep interior of Earth is more dynamic than scientists had assumed, with major structures reorganizing on timescales that, while still vast, are measurably shorter than once believed.

Yet the models do something else important: they still account for the pattern of volcanic eruptions and kimberlite activity observed at Earth's surface across the geological record. This consistency is crucial. It means the new picture of mobile, shape-shifting blobs does not contradict the evidence geologists have gathered from rocks and eruption sites. Instead, it reframes what that evidence tells us about how Earth's interior works.

The origin of the blobs themselves remains unsolved. They may be denser than surrounding mantle rock because they consist of primordial material separated out early in Earth's history—a possibility that could help explain why Earth's overall mineral composition differs from what meteorite studies would predict. Alternatively, they may have accumulated over time as dense oceanic material from subducting slabs piled up in the mantle. The models suggest that continental fragments are more likely to be transported to the African blob than the Pacific blob, a finding that aligns with recent work showing that mantle plumes rising from beneath Africa carry continental material, while those from beneath the Pacific do not.

Beyond the fundamental science, the research has practical implications. By mapping how the blobs have moved and where they are likely to be, geologists can better target the search for minerals associated with mantle upwelling. Diamonds brought to the surface by kimberlite are one example. Magmatic sulfide deposits, which contain most of the world's nickel reserves, are another. Nickel is essential for lithium-ion batteries and other renewable energy technologies. As the world transitions away from fossil fuels, understanding where these critical minerals are likely to be found becomes increasingly valuable. The blobs, it turns out, are not just monuments to Earth's deep history—they are signposts to resources the future economy will need.