A heavier ocean
Satellite maps of Earth's gravity reveal something unusual in the Indian Ocean. Around the island of Mauritius, the planet's gravitational pull is stronger than expected. This positive gravity anomaly indicates that the crust beneath the island is unusually thick and dense—like a continent instead of the surrounding oceanic floor. The island itself, a volcanic structure merely 8 to 10 million years old, is on this invisible mass. This discrepancy pointed scientists toward a radical conclusion: Mauritius is the top of a much older, hidden geological feature.
The anomaly is the remains of a 'lost' microcontinent, a fragment of land now named Mauritia. This sliver of crust was once part of the supercontinent Gondwana, wedged between the landmasses that would become India and Madagascar. Around 84 million years ago, as tectonic forces pulled India northward, this microcontinent was stretched and sank beneath the newly forming Indian Ocean. Over millions of years, the crust of Mauritia was buried under kilometers of younger volcanic rock from the Réunion hotspot, the same mantle plume that created Mauritius itself.
Crystals older than the island
The most direct evidence for Mauritia comes from tiny, durable mineral crystals called zircons. In 2013, researchers found zircons in the beach sand of Mauritius with astonishing ages, ranging from 660 million to nearly 2 billion years old. This was a puzzle, as the volcanic island is only about 9 million years old. Critics initially suggested the sand-borne crystals could have been transported by wind or as ship's ballast.
A later study in 2017 silenced these doubts. Geologist Lewis Ashwal and his team found even older zircons, some dated to 3 billion years old, embedded directly within 6-million-year-old volcanic trachyte rock on the island. This discovery was conclusive. The ancient zircon crystals must have been carried from the deep continental crust of Mauritia to the surface, carried in the magma that erupted to form the young island of Mauritius. The crystals were too old to have formed with the island and were physically locked inside its volcanic rock, proving the existence of a much older landmass hidden deep below.