The once westward roll of what is now the world's largest river was caused by a long-gone highland near what today is the river's mouth. That highland was created by the breaking away of South America from Africa and the creation of the Atlantic Ocean during the Cretaceous Period, 65 to 145 million years ago. Later, when the Andes rose up on the western side of South America, the river had no choice but to drain into the new ocean.
"It just happened in a way that the current Amazon could take advantage of where an old river and ocean basin used to sit," said geologist Russell Mapes, a doctoral candidate at the University of North Carolina in Chapel Hill.
Previous Brazilian and U.S. researchers have proposed smaller scale reversals and splits in the Amazon Basin, but nothing on the scale of the entire basin, said Mapes.
The evidence for the Amazon's ancient switcheroo comes in the form of tiny crystals of a mineral called zircon, as well as telltale signs of the river flow direction captured in the structure of old river sediments.
Zircons are stubbornly long-lived and tend to be recycled over and over without stopping their internal uranium-lead radioisotope clocks that started ticking when the minerals first formed. As a result, they are tiny windows for peaking at long-lost mountains and entire continents.
The zircons in old sands studied by Mapes, his UNC faculty advisor Drew Coleman, and their Brazilian colleagues Afonso Nogueira and Angela Maria Leguizamon Vega, stand out because they do not appear to come from the Andes at all. In fact they date to about 1.3 to 2.1 billion years ago. So they had to have been formed in rocks that solidified in mountains that eroded away into the earliest Amazon.
Mapes is scheduled to present the team's findings on Wednesday, 25 October, at the Annual Meeting of the Geological Society of America in Philadelphia. What he won't have time to describe to other researchers is the adventure they underwent to gather up those little zircons.
"It was a pretty exotic trip," said Coleman. "We took planes and aluminum small boats. In the first year we took a two-and-a-half week cruise up the river from Manaus. We sampled young and old sediment outcrops on the river. We traveled about 500 kilometers."
"In the second year, we did three small hops -- plane flights downstream then rented small boats at each stopping point," recalls Mapes. "One night in a boat we ran out of gas in an electrical storm. Luckily, it was the one place in the basin where my cell phone worked. We called the man who rented the boat to us and he came out and got us. We just bobbed around. It was a place where the river is several miles wide."
In the end, said Mapes, it was worth it to finally be able to see back further in time. "When I got the actual data back, I was happy."
WHEN & WHERE
EVIDENCE FOR A CONTINENT SCALE DRAINAGE INVERSION IN THE AMAZON BASIN SINCE THE LATE CRETACEOUS 2:00-2:15 p.m., Wednesday, 25 October 2006 Pennsylvania Convention Center Room 112 A
Ann Cairns | EurekAlert!
Large-Mouthed Fish Was Top Predator After Mass Extinction
26.07.2017 | Universität Zürich
Strength of tectonic plates may explain shape of the Tibetan Plateau, study finds
25.07.2017 | University of Illinois at Urbana-Champaign
Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers
Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...
Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.
At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...
3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects
A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
26.07.2017 | Event News
21.07.2017 | Event News
19.07.2017 | Event News
26.07.2017 | Physics and Astronomy
26.07.2017 | Life Sciences
26.07.2017 | Earth Sciences