Oldest evidence of earthquakes found in Africa
Scientists have found signs of some of the earliest known earthquakes in 3.3-billion-year-old rocks. The rocks provide early evidence of plate tectonics – Earth’s crust split into large plates that glide across the mantle. The rocks also point to what conditions may have been like when life first evolved. Geologists made the discovery after investigating the Barberton Greenstone Belt, a complex geological formation in Africa. They realised the belt is remarkably similar to much younger rocks in New Zealand that have experienced earthquake-triggered submarine landslides along the Hikurangi subduction zone. “The energy released in these earthquakes is absolutely huge, and it shakes the whole region,” said Simon Lamb, a geologist at Victoria University of Wellington.
The Barberton Greenstone Belt, named for its greenish hue, provides one of the most extensive geological records for Earth between 3.2 and 3.6 billion years ago. Researchers have struggled to understand the region because the geology is messy and it’s difficult to trace the rocks through the landscape. Cornel de Ronde, a principal scientist at a research institute in New Zealand called GNS Science, published a partial map of the belt in 2021, revealing a jumble of blocks detached from where they formed. Lamb noticed the geology was similar to what he had seen along the eastern side of New Zealand in 20-million-yearold rocks and more recent submarine landslides. In particular, the Great Marlborough Conglomerate, remnants of a continental shelf that has collapsed in submarine landslides, was strikingly similar to the bedrock of the Barberton Greenstone Belt.
Off New Zealand, the Pacific Plate is sliding underneath and rubbing against the Australian Plate, generating huge earthquakes and submarine landslides. In these landslides, rocks that formed on land and in shallow waters fall into the deep ocean, mixing up their original positions. The Great Marlborough Conglomerate formation could be the result of thousands of earthquakes over millions of years, with each earthquake shifting the largest blocks. “It’s really a record of a prolonged period of shaking,” Lamb said. “It’s showing you that this is an ongoing phenomenon in the early Earth.”
Earth formed around 4.6 billion years ago and then cooled to become a water world. There isn’t a scientific consensus on when plate tectonics began, only that it was likely over 2 billion years ago. Lamb believes that there were earthquakes before those interpreted in the Barberton Greenstone Belt and that they coincided with the origin of life.