New study hopes to settle a debate over Gondwana's breakup.
Dinosaurs roamed, mammals started to flourish, the first birds and lizards evolved, and a massive supercontinent began to split apart on Earth about 180 million years ago. Yet, the details of the breakup of one of the largest landmasses in history have stumped scientists until now.
The breakup of the supercontinent Gondwana eventually formed the continents in the Southern Hemisphere. Exactly how this happened has been debated by geologists for years. Most theories say Gondwana broke into many different pieces, but new research suggests the large land mass simply split in two.
Researcher Graeme Eagles of the University of London said he was suspicious of the theory that Gondwana had divided into many smaller continents because it was inconsistent with what is known about all other supercontinent breakups, including the breakup of Pangea into Gondwana and Laurasia.
Other continents in the geologic past, such as Rodinia, the oldest known continent, and Pangea, followed a pattern of splitting along tectonic lines into fewer, larger pieces, geologists think. Eagles wondered if a similar process could explain the breakup of Gondwana.
By studying data from where the continent first began to fracture, he determined that Gondwana split into eastern and western plates. Then, about 30 million years later, as crocodiles and sharks were evolving, the two plates split apart, and one continent became two.
Before it cracked into several landmasses, Gondwana included what are today Africa, South America, Australia, India and Antarctica. The big continents — Africa and South America — split off about 180 million to 170 million years ago. In recent years, researchers have debated what happened next, as the remaining continents rocketed apart. For example, different Gondwana reconstruction models had a 250-mile (400 kilometers) disagreement in the fit between Australia and Antarctica, an error that has a cascading effect in plate reconstructions, said Lloyd White, a geologist at Royal HollowayUniversity in Surrey, England.
With a series of computer models, the scientists tested various best fits for Australia, Antarctica and India against the compiled research data. The winner was an old-school approach, first published in the 1980s, White said. The big picture shows India, Australia and Antarctica were all joined about 165 million years ago. India started to pull away from Antarctica, first breaking away from both continents by about 100 million years ago. It zoomed north, eventually smashing into Asia. Australia and Antarctica opened up like a zipper from west to east between 85 million to 45 million years ago, White said. When the last "tooth" broke, south of Tasmania, Australia rocketed northward.