Samples extracted from beneath the sea floor by the research ship Joides Resolution suggest that the vast piece of land - called the Kerguelen Plateau - sank out of sight 20 million years ago.
Located in a remote part of the southern Indian Ocean, it is thought to have risen above the waves about 110 million years ago after a series of huge volcanic explosions.
Drilling by the Joides Resolution, the world's biggest research vessel, brought various types of volcanic rock to the surface including sedimentary rocks similar to those found in India and Australia. The discovery was made close to the Kerguelen Archipelago, a French territory of more than 80 islands midway between Africa, Antarctica and Australia.
The Joides Resolution expedition is a long-term venture run by the Ocean Drilling Programme, an international partnership of scientific institutions and government led by the US National Science Foundation. The UK is among members including Germany, Japan, Australia, Canada and China.
Scientists bored a series of holes through the plateau, which lies about two kilometres below the ocean surface.
"We found abundant evidence that much of the Kerguelen Plateau formed above sea level," said Dr Mike Coffin of the University of Texas.
"Wood fragments, a seed, spores and pollen recovered in 90 million- year- old sediment from the central Kerguelen Plateau indicates that it was above sea level."
Helen Coxall, a British palaentologist, was a member of the team examining the plankton discovered in drill core samples.
"It's a really wild part of the world. At times, the waves were 15 metres high while we were trying to look through our microscopes," she said.
Scientists believe that 50 million years ago the continent was probably covered in lush ferns, moist with tropical humidity. Small dinosaurs would have hidden in the undergrowth, stalking their prey.
Today the nearby archipelago is a haven for birds and marine mammals but the only plant life of any distinction is the Kerguelen cabbage.
Dr Coffin added: "Understanding how pieces of an ancient continent were incorporated into the oceanic environment will have significant impact on our understanding of the approximately 130 million- year-old break-up among Australia, India and Antarctica."
The drilling work also discovered evidence of massive volcanic eruptions that would have dwarfed even the most explosive upheavals recorded in modern times.
Dr Coffin said: "The scale of Kerguelen volcanism lies beyond the realm of human experience."
The power of the Kerguelen eruptions, and the amount of lava spewed out, was at least a hundred times greater than the notorious 1783 eruption of Laki in Iceland which killed three-quarters of the island's livestock and one in four people, altering Europe's climate in the process.
The ship carries about 45 scientists and is now in the Pacific Ocean exploring the deepest part of the earth's ocean, the Mariana Trench.Reuse content