The hidden fragment, dating as old as 1.3 billion years, is helping scientists trace the history of the mysterious “lost continent” of Zealandia.
As the California heat blazed outside in the summer of 2018, Rose Turnbull sat in the cool confines of a windowless basement sorting through grains of fine sand. A geologist based in New Zealand, Turnbull was in a colleague’s lab at California State University, Northridge, trying to find tiny crystals of zircon, which she hoped would help unravel secrets of the mysterious eighth continent of Zealandia, also known by its Māori name Te Riu-a-Māui.
The crystals hailed from rocks that were collected from the islands of New Zealand, which are among the few bits of Zealandia's nearly two million square miles that poke above the sea. Only recently recognized by scientists, Zealandia is the most submerged, thinnest, and youngest continent yet found. Turnbull, who works at the research and consulting group GNS Science in New Zealand, and her colleagues wanted to know more about the processes that shaped this unusual landmass.
What they found surprised them: Concealed beneath the eastern side of New Zealand's South and Stewart Islands lingers a chunk of a billion-year-old supercontinent. The discovery suggests Zealandia may not be as young as they once thought, which may bolster the case for its continental status.
"Continents are sort of like icebergs," says study author Keith Klepeis, a structural geologist at the University of Vermont. "What you see at the surface is not really the full extent of the beast."
The discovery, described in the journal Geology, may help solve a riddle that's long perplexed scientists. Most continents contain a core of rock known as a craton, a sort of geologic nucleus at least a billion years old that acts like a stable base upon which continents build. Until now, though, the oldest continental crust found on Zealandia was dated to roughly 500 million years ago - relatively youthful in geologic terms. So if Zealandia is a continent, why did its craton seem to be missing?
This newfound fragment of ancient rock may be part of the missing piece for Zealandia. The discovery "ticks the final box," Turnbull says. "We are sitting on a continent."