New maps of the lost continent of Earth
Written by Zaria GurvitReporter Features@Zaryagorvit
New research into the geology of Zealandia reveals how it formed and why it sank
In 1820, a Russian ship is crowded with sailors, and, strangely, Penguins – Heading to the men’s dinner – he saw a towering shore of ice on the horizon. This was the first ever sighting of the Fimbol Ice Shelf, and marked the official discovery of a new continent: Antarctica. It also reinforced the modern idea, supported by most maps throughout the English-speaking world, that there are seven main landmasses.
Today, schoolchildren, explorers, and politicians generally accept a strict division of the world’s land into these simple units, which include Europe, Asia, Africa, North America, South America, Australia, and Antarctica.
But in 2017, the story took an unexpected turn – the seven continents model was a fascinating one Error along. Enter Zealandia, the long-lost land to the southeast of Australia, also known as the planet Earth’s eighth forgotten continent. Scientists have long predicted the existence of this additional southern landmass, but… He remained missing for 375 years – Largely because it is almost completely submerged under 1-2 km (0.6-1.2 mi) of water. And now they are beginning to reveal its secrets.
This month, an international team of researchers released The most detailed maps Zealandia so far – encompasses all five million square kilometers (two million square miles) of this underwater area and its geology. In the process, they discovered hints about how this mysterious continent formed, and why it had been hidden beneath the waves for the past 25 million years.
Old beginning
It is believed that Zealandia has It was formed about 83 million years ago, during the Late Cretaceous period. However, its journey began up to 100 million years earlier, when the supercontinent of Gondwana – which gathered much of today’s land into one giant mass – began to break apart. As it broke up, the world’s smallest, thinnest, youngest continents came out on their own, while the areas of Gondwana that lay immediately to the northwest and southwest became Australia and Antarctica, respectively.
It is thought that all or part of Zealandia may have existed as an island for a period of time. But about 25 million years ago, it disappeared under the ocean. (Read more from BBC Future about the lost continent that took 375 years to find.)
The first real evidence that New Zealand may represent only a small, visible portion of a vast, uncharted landmass came in 2002, when scientists used bathymetry – the study of the depths of bodies of water – to determine Area analysis. The ocean above what we now call Zealandia is much shallower than the surrounding ocean, indicating that the region was not under an oceanic tectonic plate – like most of the world’s oceans – but rather a continental plate.
interval It came in 2017When scientists put together several lines of evidence, including data about the types of rocks they contain and their relative thickness — oceanic plates tend to be thinner — to suggest that this is indeed a new continent. This is not just a continental fragment or a mini-continent, as has been previously suggested, but the real deal, as 95% of it is submerged under water.
However, despite the excitement over the discovery of a new continent, and more than a decade of intense research, many details of Zealandia’s early formation have remained elusive. This is partly due to the strange event that occurred when it separated from Gondwana.
Difficult revelation
In 2019, an international team of scientists Mapping the geology of southern Zealandia. Their research revealed that at some point, Zealandia had been stretched and torn apart by tectonic forces, thinning the continent relative to normal continental plates and creating ruptures that later became oceanic crust. In the process, it became twisted, making it more difficult to reconstruct its history to reach its original form.
The researchers’ analysis of the rocks of the lost continent revealed that the expansion occurred in two stages. The first began about 89-101 million years ago, and led to the rupture that became the Tasman Sea between Australia and New Zealand. The second phase began 80-90 million years ago and led to the separation of Zealandia from West Antarctica and the formation of the Pacific Ocean. But there are still many unexplained mysteries, and the other half of this continent has not yet been studied in detail.
Gradual sinking
For the latest study, another research group — including many of the same geologists as before — North Zealandia striped.
This time, they analyzed rocks excavated from Fairway Ridge, an area in the South Pacific Ocean off the coast of Australia, which forms the northernmost tip of Zealandia. These ancient remains, which had not seen a dry day for 25 million years, included a mixture of igneous rocks – those formed as a result of volcanic processes – and sedimentary rocks that formed in shallow basins off the coast of Zealandia.
By analyzing the chemistry and radioactive isotopes found in its depths, scientists estimated the age and origins of the rocks. The oldest were gravels dating from the Early Cretaceous (about 130-110 million years ago), followed by sandstone from the Late Cretaceous (about 95 million years ago) and relatively young basalts from the Eocene (about 40 million years ago).
The resulting maps of Zealandia transform it from a featureless mass into a place with several distinct geological ranges running along its length from northwest to southeast. These fit the geology of West Antarctica Like a puzzleWhich confirms that this region and Zealandia were once interconnected.
The next stage of the investigation looked at measurements of magnetic anomalies on the ocean floor around Zealandia. These variations in the strength of Earth’s magnetic field form an invisible record of how tectonic plates have moved over time. They revealed more about the ancient expansion of the continent, which continued for millions of years and even changed direction, leading to the eventual sinking of a very thin continent.
Zealandia is finally starting to give up its secrets. But with the vast majority of this mysterious landmass lying under kilometers of water, it will take some time to uncover them all.
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