How rocks rusted on Earth and turned red

How did rocks rust on Earth and turn red? A study by Rutgers has shed new light on this important phenomenon and will help answer questions about the Upper Triassic climate over 200 million years ago, when greenhouse gas levels were high enough to serve as a model for what our planet might be in the future.

“All of the red color that we see in rocks in New Jersey and the American Southwest is due to the naturally occurring mineral hematite,” said senior author Christopher J. Lepre, assistant professor in the Department of Human Sciences. Earth and Planets from the School of Arts and Sciences at Rutgers University-New Brunswick. “As far as we know, there are only a few places where this red hematite phenomenon is widespread: one being the geological ‘red beds’ on Earth and the other the surface of Mars. Our study takes an important step forward in understanding the time it takes for redness to appear, the chemical reactions involved, and the role hematite plays. “

The research of Lepre and a scientist from Columbia University is in the journal Proceedings of the National Academy of Sciences. This challenges conventional thinking that hematite has limited use in interpreting the ancient past because it is the product of natural chemical changes that occurred long after the beds were initially deposited.

Lepre demonstrated that hematite concentrations faithfully tracked 14.5 million years of Upper Triassic monsoon rains on the Colorado Plateau in Arizona when he was on the former Pangea supercontinent. With this information, he assessed the interrelationships between environmental disturbances, climate and the evolution of vertebrates on earth.

Lepre examined part of a 1,700-foot-long rock core in the Chinle Formation in Arizona’s Petrified Forest National Park (the Painted Desert) that is in Rutgers. Professor Emeritus Dennis V. Kent of Rutgers-New Brunswick examined the same nucleus for a study conducted by Rutgers which found that the gravitational tugs of Jupiter and Venus slightly lengthen the Earth’s orbit every 405,000 years and have influenced Earth’s climate for at least 215 million years, allowing scientists to date better events like the spread of dinosaurs.

Lepre measured the visible light spectrum to determine the concentration of hematite in the red rocks. To scientists’ knowledge, this is the first time that this method has been used to study such ancient rocks, dating from the late Triassic period more than 200 million years ago. Many scientists believed that the redness was caused much more recently by iron in rocks reacting with air, much like rust on a bicycle. So, for decades, scientists considered hematite and its redness to be unimportant.

“Hematite is indeed ancient and likely results from interactions between ancient soils and climate change,” Lepre said. “This climate information allows us to sort out certain causes and effects – whether due to climate change or an asteroid impact at Manicouagan in Canada, for example – for land animals and plants when theropod dinosaurs (first ancestors of modern birds and the Tyrannosaurus Rex) were growing in importance. “

Scientists, working with members of the Navajo Nation, have submitted a multi-million dollar grant proposal to recover more carrots from the Colorado Plateau which will include rocks known to record very rapid atmospheric change in carbon dioxide. similar to its recent doubling as a result. of human activity.