The Earth's interior has always been a source of great mysteries and challenges for geologists around the world. Recently, scientists discovered new evidence on Easter Island that calls into question long-held theories about the behavior of the Earth's mantle. The island, famous for its iconic Moai statues, also hides much older secrets beneath its surface. New findings suggest that the volcanoes in this area could have been active much longer than previously thought, in a way that challenges the 'conveyor belt' theory of the Earth's mantle.

In 2019, a team of geologists from Cuba and Colombia, led by Dr. Yamirka Rojas-Agramonte, traveled to Easter Island to conduct a detailed study of the island's volcanic history. Their mission was to date volcanic rocks in order to better understand the timeline of volcanic activity in the area. They expected to find minerals that were around 2.5 million years old, which was the previous estimate for the age of the lava found on the island. However, instead, they discovered zircons, minerals that are as much as 165 million years old—causing shock among the researchers.

The scientific importance of zircons

Zircons are crucial for determining the age of geological layers because they contain uranium, an element that decays into lead over time. By measuring the ratio of uranium to lead in zircons, scientists can accurately determine when these minerals formed. This dating method is often used in geology because it provides precise results about the age of minerals, and in the case of Easter Island, the discovery was an incredible surprise.

The oceanic plate beneath Easter Island is about 2.5 million years old, meaning these ancient minerals are significantly older than the plate itself on which the island sits. This raises questions about how these minerals ended up here and where they originated. Chemical analysis showed that these ancient zircons have a similar composition to modern volcanic minerals, leading researchers to conclude that these minerals originated from deep parts of the Earth's mantle—long before today's volcanoes began to erupt.

This discovery prompted a reassessment of existing theories about how the Earth's mantle functions. The volcanoes on Easter Island are part of so-called 'hotspots'—regions of the Earth's crust that are persistently exposed to thermal influences from deeper mantle layers. The 'hotspot' theory explains the formation of volcanoes like those in Hawaii and Easter Island. According to this theory, the Earth's plates move over these hotspots, while the hotspots remain stationary deep in the mantle, creating a chain of extinct volcanoes with a few active ones at the end of that chain.

The 'conveyor belt' theory called into question

However, the presence of zircons that are 165 million years old on Easter Island suggests that the hotspot beneath the island may have been active much longer than previously thought. According to the classical theory, the Earth's mantle functions like a conveyor belt that transfers heat and materials, but these findings suggest that a part of the mantle could remain static for thousands, or even millions, of years. This would mean that the Earth's mantle does not behave as we have previously believed, opening up new possibilities for exploration.

To confirm this theory, Dr. Rojas-Agramonte consulted Dutch geologist Douwe van Hinsbergen, an expert on subduction zones, areas where oceanic plates sink beneath neighboring plates, returning to the Earth's mantle. Van Hinsbergen's reconstructions of past geological events indicated that there was a large volcanic plateau near Easter Island about 165 million years ago, which later disappeared beneath Antarctica around 110 million years ago. This reconstruction suggests that the hotspot could have been active for a long time.

Impact on future geological research

The discovery of ancient zircons on Easter Island has significant implications not only for understanding the history of volcanic activity on this island but also for global geological theory. If these minerals really have remained in the same area for so long, it means that the theory of the Earth's mantle as a 'conveyor belt' could be incorrect or at least incomplete. This discovery raises new questions about how the Earth's mantle actually functions, especially in hotspot areas.

This discovery also has important implications for other regions of similar volcanic activity, such as the Galapagos and New Guinea. In these areas, geologists might find similar evidence of prolonged activity in hotspots, further confirming the new theory about the behavior of the Earth's mantle. Additional research is needed to understand why parts of the mantle remain static while the rest of the Earth's crust moves above them, and how this affects the formation of volcanic chains.

As research continues, Easter Island becomes a key location for studying the dynamics of the Earth's mantle. These findings not only change our understanding of the Earth's inner layer but could also have far-reaching consequences for the entire field of geology. In the future, geologists will need to develop new models that take into account these static regions of the mantle, leading to a better understanding of how the Earth functions beneath our surface.

Source: Utrecht University