The Place Where Life Turned to Stone

In Science by Anja, February 8, 2017

Littering the landscape in Chubut province, southern Argentina, are strange stone monuments to life that thrived up to 65 million years ago. The province is home to rare “petrified forest” – where life has turned to stone.

“Many people find the area moonlike and eerie,” says Dr Peter Wilf, Professor of Paleobotany, Penn State University in the US, of Patagonia’s petrified forests, adding, “To me, it is spectacularly beautiful.”

It is places like these, where rocks full of fossils are actually exposed at the surface that reveal the story of life on Planet Earth

“There is almost no modern vegetation, it is very dry, and the winds are extremely strong. I am a big guy, and sometimes even I get blown down.”

Petrification is when an animal or plant’s organic matter is replaced by minerals and it eventually “turns to stone”

The process preserves natural forms in minute 3D anatomical detail.

Dr Wilf and a team from the US and the MEF (Museo Paleontológico Egidio Feruglio) in Argentina have studied Patagonia’s petrified forests and fossil-rich lands for 16 years.

Chubut’s Ormachea Park is considered one of the most important sites.

Unique dinosaurs, fossilised mammals, as well as plants, flowers and fruits from “nearly every geologic time period” are found in Chubut.

But perhaps Ormachea’s most bizarre and eye-catching ancient monuments are the huge petrified tree trunks.

“Petrified wood in Argentina“

“Very tall conifers and flowering trees” that lived along rivers near the South Atlantic coastline about 65 million years ago “not long after the last dinosaurs went extinct”, are scattered across the landscape, says Dr Wilf.

But these trees did not grow here. They were transported by water when riverbanks on which they lived eroded during storms, ending up in sand estuaries where they were buried by layers of sediment. Over time, dissolved silica replaced the trees’ organic materials. And increasing temperature and pressure turned the trees and encasing sands to stone.

“Much later, geologic uplift brought these petrified trees back to the surface of the Earth,” explains Wilf. “And erosion removed all the overlying sediments, exposing the beautiful, enormous fossils.”

“Petrified wood with the internal structure of the tree still maintained” by Moondigger is licensed under CC BY 2.5

So Ormachea Park is not a “petrified forest” in the true sense, because its trees are not where they would have originally grown.

Yet this extraordinary site is among the most important in paleobotany: it gives rare insight into the time immediately after dinosaurs were wiped out at the end of the Cretaceous Period, having dominated the Earth for 165 million years.

Each petrified forest tells a different story

Further south, Cerro Cuadrado is a spectacular and famous Middle Jurassic fossil site where colossal trees have remained in their original position.

Huge tree trunks and ancient monkey puzzle trees are among the specimens found here.

“Unlike Ormachea Park, the Cerro Cuadrado trees were blown down by Jurassic volcanic eruptions and fossilised very close to where they grew, so it is a true fossil forest,” Wilf says.

It is a palaeontologist’s treasure trove but has also been plundered by fossil smugglers.

According to Dr Wilf, large numbers of prehistoric pine cones from Cerro Cuadrado – which are often exquisitely preserved in their original shape, with great scientific value – have been sold on the black market. Dr Wilf says the fossil forest is now protected, but illegal sales still happen.

Petrified wood is fairly common but entire petrified forests are rare

Other than in Argentina, famous petrified forest sites include on the Greek island of Lesbos. And in the US, Utah, Arizona and Wyoming are home to some of the best examples of petrification.

“Petrified Forest National Park, Utah, USA“ by Diego Delso is licensed under CC BY 3.0

The exposed, windswept and rugged landscapes of Patagonia keep Dr Wilf hooked to this region: “It is places like these, where rocks full of fossils are actually exposed at the surface that reveal the story of life on Planet Earth.”

Article cover photo:
“Petrified logs” by Jonathan Zander is licensed under CC BY 3.0