For many years, scientists have believed that the Earth’s mantle – the layer beneath its surface – moves like a giant conveyor belt, carrying heat and material that form volcanoes.
But new research from Easter Island challenges this idea and suggests the Earth’s mantle may behave quite differently.
Easter Island, famous for its large stone statues, is made up of several extinct volcanoes.
Geologists have known that the island’s oldest lava deposits are about 2.5 million years old, but recent discoveries show something surprising.
A team of Cuban and Colombian geologists, led by Dr. Yamirka Rojas-Agramonte, went to Easter Island in 2019 to study the island’s volcanic history.
They used a technique that dates zircon minerals found in the lava to determine when the volcanoes erupted.
Zircon minerals are special because they contain uranium, which slowly changes into lead over time. By measuring the amount of uranium and lead in the minerals, scientists can figure out how old they are.
The team expected to find zircons that were around 2.5 million years old, but instead, they found something unexpected – some of the zircons were as old as 165 million years!
This discovery puzzled the researchers. The oceanic plate underneath Easter Island is not nearly that old, so how could these ancient minerals have formed on the island?
Further chemical analysis showed that the composition of the old and new zircons was the same, suggesting they all came from the same type of magma.
This means the zircons likely originated from deep in the Earth’s mantle long before the Easter Island volcanoes even formed.
The team realized that these ancient minerals could have come from the Earth’s mantle, where the magma that forms hotspot volcanoes originates. Hotspot volcanoes, like those on Easter Island and Hawai’i, are formed when large blobs of rock rise from deep within the Earth’s mantle, creating volcanoes when they reach the surface.
Scientists have long believed that these mantle plumes stay in the same place for millions of years, while the Earth’s surface (its tectonic plates) moves above them. This explains why we see lines of extinct volcanoes in places like the Pacific Ocean, where only the youngest volcanoes are still active.
But the discovery of ancient zircons on Easter Island raised the question: could the mantle plume beneath the island have been active for over 165 million years?
To answer this question, Dr. Rojas-Agramonte worked with Douwe van Hinsbergen, a geologist from Utrecht University.
He specializes in studying how tectonic plates move and where they disappear into the Earth’s mantle in subduction zones – areas known for earthquakes and volcanoes.
Van Hinsbergen’s research showed that there used to be a large volcanic plateau near Easter Island 165 million years ago, but it disappeared under the Antarctic Peninsula about 110 million years ago.
This discovery suggests that the mantle plume beneath Easter Island has been active for a very long time.
This finding creates a new problem for scientists. For years, geologists have believed that the mantle moves with the Earth’s tectonic plates, but the ancient zircons found on Easter Island suggest that parts of the mantle, including mantle plumes, may not move as much as we thought.
If the mantle were moving with the plates, those ancient minerals should have been carried away long ago. Instead, they have stayed in place, suggesting that the mantle around the plume may be more stationary than previously believed.
This new discovery challenges the traditional “conveyor belt” theory of mantle movement and could change how scientists think about the Earth’s interior. It suggests that the Earth’s mantle moves much more slowly than previously assumed, and this finding has big implications for our understanding of Earth’s geological history.
The team’s research on Easter Island is helping to reveal new clues about how our planet’s mantle behaves, and it may also provide answers to questions about other volcanic regions, such as the Galapagos Islands and New Guinea.
