Zealandia: Earth’s lost eighth continent has been found

Beneath the waves of the South Pacific lies Zealandia, a submerged landmass spanning nearly two million square miles. Often referred to as Earth's potential eighth continent, 95% of its surface lies underwater.

Once part of the ancient supercontinent Gondwana, Zealandia’s fragmented history provides a unique window into the tectonic evolution of our planet.

Zealandia’s story begins over 100 million years ago during the breakup of Gondwana. This supercontinent, which once included modern-day Africa, South America, Antarctica, Australia, and the Indian subcontinent, experienced a gradual fragmentation.

Around 85 million years ago, South Zealandia split from West Antarctica. By 60 million years ago, North Zealandia detached from Australia.

Unlike its neighboring continents, Zealandia did not remain above water. During the Paleogene period, cooling and thinning of its crust caused Zealandia to sink, leaving New Zealand and New Caledonia as its only visible remnants. Today, the Pacific-Australia plate boundary divides Zealandia into northern and southern regions.

The existence of this submerged continent was first proposed decades ago, but recent advances have brought Zealandia to scientific prominence. A study published in Tectonics by researchers from GNS Science, led by geologist Nick Mortimer, marks a significant breakthrough.

The team conducted geological surveys across the northern stretches of Zealandia, employing advanced dredging techniques. They collected a range of rock samples from the Fairway Ridge to the Coral Sea, including sandstone, mudstone, limestone, and basaltic lava. These samples provided crucial insights into Zealandia's geological timeline.

“By dating these rocks and analyzing their magnetic anomalies, we mapped the major geological units of North Zealandia,” the team explained. This marked the completion of the first comprehensive offshore geological mapping of the Zealandia continent.

The retrieved rocks tell a captivating story. Some sandstone samples date back approximately 95 million years to the Late Cretaceous period. Granite and volcanic pebbles from as far as 130 million years ago reveal Zealandia's Early Cretaceous past. Basalt samples, meanwhile, represent more recent history, originating from the Eocene epoch around 40 million years ago.

These findings challenge previous assumptions about Zealandia’s formation. Conventional theories suggested a strike-slip breakup, where tectonic plates slide past each other horizontally.

However, Mortimer’s team proposed a different scenario. They believe plate stretching created subduction-like fractures, leading to the formation of the Tasman Sea. Subsequent tectonic activity further thinned Zealandia’s crust, relegating it to an underwater existence.

The implications of Zealandia’s geological evolution extend beyond academic interest. Understanding its unique features, such as crustal thinning up to 65%, sheds light on broader tectonic processes. These insights also highlight Zealandia’s role in shaping the Pacific region's dynamic geology.

According to a GNS Science researcher, “Zealandia’s underwater status in no way diminishes its geological significance.” Its vast expanse and diverse rock formations make it a valuable natural laboratory for studying Earth's tectonic history.

Zealandia remains an active area of research. Its submerged status poses challenges, but advances in technology, such as deep-sea dredging and seismic imaging, continue to unlock its secrets. Ongoing studies aim to refine our understanding of this hidden continent, offering a more comprehensive picture of Earth's geological past.

As scientists continue to explore Zealandia, they not only reveal the continent's mysteries but also enhance our understanding of the planet’s ever-evolving story.

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