The continents we know are not stable entities. According to a study published in
Nature Geoscience, their base undergoes continuous erosion from movements in the Earth's mantle. Fragments of the continental crust are torn away from depths greater than 150 kilometers (93 miles) and then transported horizontally over distances that can exceed one thousand kilometers (621 miles). This extremely slow process permanently alters the composition of our planet's deep layers.
This discovery sheds new light on the formation of volcanic islands in the middle of oceans. Regions like Christmas Island in the Indian Ocean show chemical signatures surprisingly similar to those of continents, even though they're surrounded by vast oceanic expanses. Researchers have long sought to understand how these continental elements could end up so far from their place of origin.
Our planet reveals a previously unknown dynamic: continents are gradually losing their base, sending ancient materials to drift beneath oceans where they fuel new volcanic activity.
Credit: Prof Tom Gernon, University of Southampton The international team, led by the University of Southampton, developed computer simulations to model the behavior of continents and the Earth's mantle. Their work shows that waves propagate at the base of continental masses, creating instabilities that gradually tear away pieces of their deep root. This movement occurs at an infinitesimal speed, much slower than fingernail growth.
Analysis of geochemical data from the Indian Ocean provided concrete evidence of this mechanism. Scientists studied the surroundings of the Indian Ocean seamounts, formed after the breakup of the supercontinent Gondwana more than one hundred million years ago. They observed that immediately after this separation, a significant increase in magma enriched with continental elements appeared at the surface.
Over tens of millions of years, this chemical signal gradually faded as the supply of continental material decreased. This evolution occurred without the involvement of the deep mantle plumes that geologists had previously considered responsible for this type of volcanic activity. The discovered process operates independently of these upwellings of hot material from the depths.
This research opens new perspectives for understanding the long-term evolution of our planet. The described movements persist long after the apparent separation of continents, continuing to shape the composition of the Earth's mantle and influencing volcanic activity over geological timescales. Our understanding of Earth's internal dynamics is significantly enriched.
The chemical signature of rocks: the geological passport of continents
Each region of Earth possesses a unique chemical signature that allows scientists to trace its history. Continents show particular concentrations of certain elements like potassium, uranium, or thorium, which clearly distinguish them from oceanic rocks. These chemical differences serve as true fingerprints to identify the origin of materials.
When continental fragments are transported toward the oceanic mantle, they retain this characteristic signature. Volcanoes that erupt in oceans and incorporate this torn continental material then produce lavas whose chemical composition betrays this origin. This is how isolated volcanic islands can show surprising chemical similarities with distant continents.
Geochemists analyze these signatures with remarkable precision, measuring ratios between different elements and isotopes. These analyses not only identify the presence of continental material but also estimate its age and geographical origin. Each sample of volcanic rock thus becomes a valuable witness to deep processes.
The persistence of these chemical signatures over tens of millions of years offers scientists a unique window into our planet's geological history. It allows reconstruction of past movements of continents and the mantle, revealing unsuspected connections between regions now separated by entire oceans.