Gondwana really was a supercontinent. And it helped kick-start life on Earth
The discovery of Gondwana’s buried bits helps settle the question of whether it was a supercontinent.
550 million years ago, Earth appeared vastly different from today. The Southern Hemisphere was dominated by a single continent called Gondwana. Geologist Eduard Seuss identified Gondwana in 1885, based on a unique plant fossil discovered in what is now India. The same fossil was later found in Australia, Africa, Antarctica, and South America, proving these land masses were once connected.
The debate over whether Gondwana was a supercontinent has been ongoing. A new paper I coauthored, published in Science Advances, may finally settle the dispute. We discovered a previously hidden portion of the Gondwanan landmass buried beneath mountains, indicating it was significantly larger than previously thought.
To define a supercontinent, geologists identified cyclic, global-scale sea level changes in the geological record, which date back at least 2 billion years. Four supercontinents have been recognized since the 1980s: the youngest being Pangea, which formed 300–250 million years ago; Gondwana, the second youngest, at 550–500 million years; Rodinia, which formed about 1 billion years ago; and the oldest verified, Columbia or Nuna, which formed between 2–1.6 billion years ago.
However, Gondwana's supercontinent status has been questioned in recent years. This was because the arbitrary threshold of 75% continental landmass was not met, with Gondwana initially measured at 64%. While additional landmasses were added, they were still insufficient to elevate Gondwana to supercontinent status.
Our serendipitous discovery was made while compiling a global dataset of granite samples to understand how deep crustal processes relate to mineral formation. Many granites are formed by melting older continental rocks. We used a technique to measure radioactive isotopes in rocks, which has existed for decades. We plotted the individual data points at a continental scale to create an age-map of the deep Earth.
Our analysis revealed that all Himalayan granites were derived from a common continental block that formed between 700–550 million years ago and was part of Gondwana.
When Gondwana was forming between 750 and 550 million years ago, it was a frozen, arid landmass with Himalayan-sized mountain ranges crisscrossing it. Once the continental fragments merged, Earth had to reconfigure its plate tectonics. A volcanic arc chain formed around Gondwana, encircling it from Russia via China, Australia, Antarctica, South Africa, and the Andes of South America. This volcanic arc around Gondwana was the precursor of today's Ring of Fire around the Pacific Ocean, with a length almost 35,000km.
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