Some scientists think The Nile can reveal the mysteries of the mantle beneath it.
It has been debated over the Nile age – whether it formed from a river that diverted about 5 million years ago or whether a proto-Nile has flowed through the area for 30 million years. If the Nile is older, as a team of researchers' evidence suggests, it may reflect the course of a plume of mantle material circulating beneath it. Mantensmile is the largest layer of The earth, which consists of high-pressure rock under the earth's crust and above the core.
"Maybe we can use rivers to understand how the mantle flows" more generally, Claudio Faccenna, the study's first author and professor at the University of Texas at Austin, told Gizmodo.
Two competing models try to explain the Nile. In one, the Nile was formed when a drainage basin changed its course from west to north about 6 million years ago, due to the same processes that formed a crack in the African tectonic plate called the East African Rift. The second theory says that the river was formed 30 million years ago as a result of long-standing geological processes in the mantle that have pushed the soil upwards in Ethiopia and downwards closer to the Mediterranean.
The team of researchers from the United States, Canada, Italy and Israel presented new evidence for the latter theory, including data and modeling. The modeling of how the local topography changed over time suggests that the Ethiopian plateau may have started to build up 30 million years ago, while the country began to descend into the eastern Mediterranean, by the Nile. The researchers linked this model to one of the mantles moves as large stone slabs alternate around paper published today in Nature Geoscience.
Previous research from this team also supports an older Nile. Analysis of 20 to 30 million year old rocks, called zircons found at the mouth of the Nile, showed that they appear to match the rocks of the Ethiopian plateau at the source of the Nile, indicating that the river is at least as old. The thickness of the sediment, as well as the erosion of the Blue Nile (one of the most important tributaries of the Nile) also seems to support the older age.
On the other hand, the researchers say they have shown that some rivers can serve as a tool for understanding the mantle behavior below. Some rivers usually come from mountains or high plateaus, but others, such as the Nile or Yenisei River in Siberia, simply begin in places with higher ground where the mantle of the earth has shot up. These types of rivers differ in the type of sediment they deposit on theirs mouth (usually it is of volcanic origin, from the mantle).
This work is exciting for researchers like Faccenna who hope to understand better mantle, which is difficult to study because of its depth under the earth's crust. "If we can find another signal about the deep mantle on the surface, it would be fantastic," he told Gizmodo.
Obviously, this work is based on a model, so there are built-in human assumptions that can change its results. But I really like the idea that there are rivers here on earth that we can use as windows for the underground.