Tens of millions of years after it disappeared under the waters of the Pacific Ocean, scientists have completed the first explorations of what some scientists are calling a hidden continent, Naaman Zhou reports at the Guardian.

During a two-month ocean voyage this summer, a team of more than 30 scientists from 12 countries explored the submerged landmass of Zealandia on an advanced research vessel and collected samples from the seabed. Scientists were able to drill into the ocean floor at depths of more than 4,000 feet, collecting more than 8,000 feet of sediment cores that provides a window into 70 million years of geologic history, reports Georgie Burgess for ABC News.

More than 8,000 fossils from hundreds of species were also collected in the drilling, giving scientists a glimpse at terrestrial life that lived tens of millions of years ago in the area. "The discovery of microscopic shells of organisms that lived in warm shallow seas, and of spores and pollen from land plants, reveal that the geography and climate of Zealandia were dramatically different in the past," expedition leader Gerald Dickens said in a statement. While more than 90 percent of Zealandia is now submerged under more than a kilometer (two-thirds of a mile) of water, when it was above the surface, it likely provided a path that many land animals and plants could have used to spread across the South Pacific, notes Naaman Zhou of the Guardian.

The Geological Society of America officially endorsed the long-standing theory that a nearly 2 million-square-mile section of Pacific Ocean floor around the country of New Zealand was actually continental crust that had submerged beneath the water in a paper published by its journal in February. As Sarah Sloat reports for Inverse, this sinking, believed have taken place after the continent broke off from Australia around 60 to 85 million years ago, made New Zealand, and other seemingly disparate islands in the area, the remains of what was once a large landmass.

However, classifying Zealandia as a continent is still a source of debate among scientists. In an interview with Michael Greshko of National Geographic in February, Christopher Scotese, a Northwestern University geologist was skeptical. “My judgment is that though Zealandia is continental, it is not a continent,” Scotese said. “If it were emergent, we would readily identify it with Australia, much like we identify Greenland with North America and Madagascar with Africa.”

Scientists now plan to study the sediment cores and fossils to help create models of how the region looked and changed over the course of tens of millions of years, reports Sloat, and plans are always in the works for a return expedition next year.