How can a part of a continent be found at the bottom of the sea, which was formed only over 2 billion years later?
Scientists at a geological laboratory in Beijing, China, have recently analyzed rocks dating back approximately 2.8 billion years provided by Dr. Henry Dick, a senior scientist at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, USA.
The results indicate that the rock material not only dates back to the Archaean era of 2.8 billion years but also has the potential to reveal how the Earth’s interior operates. Before measuring the chemical composition of the 2.8 billion-year-old samples, the team of scientists observed that, to the naked eye, they resembled something from a continent rather than from the ocean floor.
Rocks dating back approximately 2.8 billion years provided by Dr. Henry Dick. (Illustrative image).
Ross Mitchell, a co-author of the study, stated: “We found very resilient materials when melted or mixed. Such a component indicates the Archaean era from 4 to 2.5 billion years ago.” However, how could a portion of the continent be “timelessly suspended” at the bottom of the sea, where it only formed more than 2 billion years later?
The study suggests that the most plausible explanation is that the rocks broke away from the southern part of the ancient African continent and drifted through the upper layer of the Earth’s crust for over 2,000 kilometers before finally appearing at the Southwest Indian Ridge – where Dr. Henry Dick’s team retrieved them.
The upper layer of the Earth’s crust – known as the lithosphere – is soft and hot, unlike the hard crust and asthenosphere above it. The lithosphere extends from about 100 km to around 700 km below the Earth’s surface. The asthenosphere not only allows the crust and lithosphere to move around but also acts like a powerful mixer to blend everything at temperatures around 1,300 degrees Celsius. If the scientists’ hypothesis is correct, it would challenge a common principle that the universe is chemically homogeneous.
Therefore, they are actively seeking more evidence to support their hypothesis, as a previous article in the journal Nature in 2008 also discussed the surprisingly discovered ancient continental rocks found beneath the younger seabed.
With funding from the U.S. National Science Foundation, scientist Henry Dick has led and participated in over a dozen expeditions since the 1970s to map and sample the Southwest Indian Ridge, an underwater mountain range stretching over 7,000 km, dividing the seas between Africa and Antarctica.
The deepest point ever drilled through the oceanic crust, during the second leg of an expedition led by geologist Henry Dick of WHOI in 2006, was drilled 1,500 meters beneath the Atlantis tectonic plate, an area of the Indian Ocean where the lower crust is exposed.
