Dose of STEM: Hidden Continents

Introduction

When defining a continent, there is very little science involved. A continent is usually defined based on size, continuity, and separation by the ocean; however, these parameters are left vague and the definition is generally dependent on the 7 already established continents. For geography being categorized as both science and humanities, the definition of a continent is not a scientific one. But a single lackluster definition is not enough to write off an entire subject as “not science-y enough.” When discovering and proving “new” continents exist, geography is used in conjunction with geology, geochemistry, and geophysics to prove that these continents are not new; instead, they are just hidden.

Zealandia

Zealandia is the newest hidden continent to be recognized by scientists. In 2017, a team led by Nick Mortimer proposed naming Zealandia a continent based on the rock composition of the area. The seafloor around New Zealand is largely silica, which is associated with continental crust rather than the typical magnesium- and iron-filled rocks of oceanic crust. It is also notably thicker and elevated compared to the typical seafloor found nearby. Even with this geologic evidence, the team noted the conspicuous lack of a craton. A craton is the billion-year-old core of a continent and until recently, the oldest part of Zealandia found was approximately 500 million years old. A new study, however, has found parts around 2.7 billion years old. Researchers collected 169 rock samples from around New Zealand, crushed them into grains, and sorted them by both density and magnetics until all that was left was fine sand of zircon crystals. They then modeled the age of the zircons and the parent rock the zircons formed from. At 1.3 billion years old, the zircons existed at a time when the supercontinent Rodinia would have been formed, creating magma pockets that would one day become the craton of Zealandia. The zircons were also found to have notably low levels of the isotope Oxygen-18 which is uncommon in the granite rocks they were found in. The levels of O-18 allow researchers to theorize the origin process of Zealandia and by extension, suggest the continent is older than once thought. Despite this, Zealandia is still the youngest, thinnest, and most submerged of the main continents around today, and of its 2 million square mile expanse, the islands of New Zealand and New Caledonia are some of the few parts to be above sea level.

Greater Adria

Greater Adria is an ancient piece of continental crust that was demolished millions of years ago. Although the continent is now fractured, its pieces can be found across 30 countries including mountains in Italy, Greece, Turkey, the Alps, and the Balkans. In order to find the remnants of Greater Adria, geologists reconstructed the tectonic movements of the last 240 million years. Geological and geophysical data collected over the course of 10 years was plugged into a software called “GPlates” (a program anyone can use for free) so researchers could visualize the data and unlock the history of Greater Adria. Starting 240 million years ago, Greater Adria was part of the supercontinent Pangea and located next to modern-day Northern Africa and Southwestern Europe. After 20 million years it broke apart from Northern Africa and another 40 million years after that it broke away from Southwestern Europe becoming an isolated continent. Approximately 100 million years ago, the destruction of Greater Adria began. It slowly began to slide beneath the continental plates of Southern Europe, scraping off the top layers of sedimentary rock into the notable mountain ranges of modern Europe. Apart from the Adria region of Italy, the majority of Greater Adria is now 932 miles below ground but even in its inaccessible state, its remnants continue to shape European geography.

Icelandia

Icelandia is a hidden continent that has been proposed as a way to explain the abnormal features of the ocean floor and the thickness of the crust surrounding Iceland. The proposed area of Icelandia stretches from Greenland to Scandinavia with Iceland being the last remaining part above sea level. The currently accepted model for the creation of Iceland is that about 60 million years ago a volcano erupted creating the island in the middle of the Northern Atlantic. Rather than the traditional explanation for the formation of the Northern Atlantic Ocean and Iceland, the theory proposing Icelandia suggests something completely new. According to the research team, the ocean formed from the North and South leaving an unbroken horizontal strip of dry land connecting modern-day Greenland and Scandinavia. About 10 million years ago, the east and west of the land bridge were submerged leaving modern-day Iceland. This new proposal for the creation of Iceland would explain why the continental crust beneath the island is 5-7 times thicker than expected from a volcanic eruption and it could be relevant to the similarity of fossil records across the region. Despite the proposed evidence for Icelandia, many geologists are skeptical and waiting for more proof to back the theory. More research is planned following the COVID-19 pandemic. However, even if the theory of Icelandia gets disproven, it will have contributed to science by encouraging more research on the subject and challenging the accepted model of the creation of Iceland.

Mauritia

Mauritia, the continent hidden below Mauritius, was discovered when researchers found 3 billion-year-old zircons on an island where the oldest rocks are 9 million years old. Ancient zircons were first found on the island in 2013. However, they were not sufficient proof due to their location in beach sand that could easily have been carried by the wind from far away. More recently, however, research teams found zircons inside rocks proving there is ancient continental crust beneath Mauritius. The crust beneath the island originates from the breaking of the supercontinent Gondwanaland approximately 200 million years ago and it was forced to sink below the Indian Ocean approximately 84 million years ago. The few sections remaining above sea level were created by underwater volcanic eruptions which were responsible for pushing zircons to the surface. The hidden continent of Mauritia also explains the variations in the gravitational pull of the region and it suggests there may be other hidden continents below the Indian Ocean.

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