Unveiling the Hidden Secrets of Ancient Star Dunes Through Radar Discovery

Sign up for CNN’s Wonder Theory science newsletter to delve into the universe with updates on exciting discoveries and scientific progress.

Marvel at the magnificent star dunes that dominate vast desert landscapes. These towering sand dunes, shaped like pyramids, are some of the tallest on our planet. They are formed by winds blowing from different directions, crafting spiral-shaped sand ridges that spiral outwards from a central peak.

While star dunes are commonly found in sandy deserts worldwide, scientists have long wondered about their formation and their puzzling absence in the geological record.

Brian Hynek

Related article

Rare rock formations might offer insights into potential life on ancient Mars. A recent study of a star dune in Erg Chebbi, a part of the Sahara Desert in Morocco, has uncovered new details about its age and development. This discovery suggests that evidence of ancient star dunes could have been present in plain sight all this time.

Using radar scans and analysis of sand grains buried deep inside the star dune, scientists mapped the mound’s internal structure. The researchers calculated that the oldest part of the dune’s base formed around 13,000 years ago. But for about 8,000 years, the research team discovered, the star dune — which covers 0.4 miles (700 meters) and stands 328 feet (100 meters) tall — didn’t grow much at all. In fact, most of the growth to its present size took place over the past 1,000 years, much more rapidly than expected, researchers reported March 4 in the journal Scientific Reports.

“I found their results very interesting because, like most people, I had not suspected that star dunes could accumulate so quickly,” Andrew Goudie, a professor emeritus of geography at the University of Oxford in the United Kingdom, told CNN in an email. Goudie, who was not involved in the new research, coauthored a study published in March 2021 that analyzed the global distribution of star dunes.

The scans from the new study showed that the dune was shifting its position. According to Geoff Duller, a coauthor of the study and chair of the department of geography and Earth sciences at Aberystwyth University in Wales, the dune is moving at a rate of about half a meter per year. Duller pointed out that this movement indicates that star dunes are just as active as other types of dunes.

“Knowing how fast these things are moving is quite important for infrastructure in these areas,” as their migration could affect construction of roads or pipelines, he added.

Below the surface

The new research focused on the Erg Chebbi star dune named Lala Lallia, meaning “highest sacred point” in the local Berber language. Charles Bristow, a sedimentology professor at Birkbeck College in the University of London, led the study. He worked with a group of geology students to map the dune. They collected data by walking over Lala Lallia and pausing every 1.6 feet (0.5 meters) to use ground-penetrating radar, which was challenging in the shifting sands, as Bristow explained to CNN via email.

Geology students from the University of London's Birkbeck College survey the star dune at Erg Chebbi.

Geology students from the University of London's Birkbeck College survey the star dune at Erg Chebbi.

Charlie Bristow

When the radio waves bounced back to the receiver’s antenna, they created detailed images revealing the shapes of various sediment layers beneath the researchers’ location, as explained by Bristow.

The next step involved gathering sand samples from different depths to determine the deposition timeline of the sands. This process required the scientists to extract tubes of sand cores from Lala Lallia by using hollow pipes made of metal or plastic, hammered into the dune. This resulted in small tubes of sand enclosed in an opaque container. In the laboratory, researchers examined individual sand grain crystals of quartz and feldspar to measure the environmental radiation accumulated over thousands of years in the dune’s depths, as described by Duller.

“There’s radioactivity everywhere, at very low levels,” Duller said. “Some of it gets stored within the crystals.”

David C. Catling

Related article

A shallow lake in Canada may hold clues to the origins of life on Earth. Exposure to daylight quickly removes radiation from the crystal reservoirs in just 10 to 30 seconds. However, once sand grains become buried, they start accumulating radiation from the surrounding environment. In a laboratory at Aberystwyth, scientists used a technique called optically stimulated luminescence dating to determine the age of collected grains. By making the grains release their stored energy as light and analyzing the light intensity, researchers were able to calculate how long the crystals had been in darkness. This involved shining a light on the minerals to release trapped electrons, which produced a luminescent signal that was measured to determine the crystals' age.

Duller explained that the age of sediment can be determined by the brightness of light. The research team measured the brightness of grains at various depths in the dune to figure out when the structure was initially formed, when it experienced its most significant growth, and how fast it moved.

This discovery helped solve a mystery.

Geologists have long been puzzled by the absence of ancient evidence of star dunes in desert environments. These environments usually preserve their history well, with dunes leaving behind clues in layers of compressed sandstone. However, the discovery of star dunes is extremely rare, with only one known example found in Scotland dating back to the Permian-Triassic period around 251.9 million years ago.

"Why is that? Where have all the star dunes gone?" Duller asked. The scientists explained that the disappearance of star dunes may be due to a matter of perspective. They suggested that the large size of star dunes could have led to eroded parts being mistakenly identified as separate remnants of other types of dunes.

Duller pointed out that when examining individual pieces of a star dune in the geological record, they may resemble something else. However, when all the pieces are put together - with large troughs of cross-bedded sands in the middle and arms stretching out in each direction - it becomes clear that it is indeed a star dune.

On the Giza Plateau, situated on the west bank of the Nile River near modern-day Cairo, stands the Great Sphinx of Giza. This impressive statue features the body of a lion and the head of a human. The Great Sphinx is believed to have been constructed by the ancient Egyptians in the 3rd millennium BC, specifically between 2520 BC and 2494 BC. It is considered one of the largest single-stone statues in the world. The mystery surrounding the identity of the model used for the face and the builders of this monument has led to it being called the "Riddle of the Sphinx," a reference to its Greek counterpart. However, it is important to note that this phrase is not directly linked to the original Greek legend.

The Great Sphinx of Giza, a large half-human, half-lion Sphinx statue on the Giza Plateau on the west bank of the Nile River, near modern-day Cairo seen with the Chephren (Khafre) Pyramid in the background, 23 October 2007. The Great Sphinx is one of the largest single-stone statues on Earth, and is commonly believed to have been built by ancient Egyptians in the 3rd millennium BC, somewhere between 2520 BC and 2494 BC. The debate surrounding the real-life model used for the face when it was built, and by whom, have earned the title "Riddle of the Sphinx," a nod to its Greek namesake, although this phrase should not be confused with the original Greek legend. AFP PHOTO/CRIS BOURONCLE (Photo credit should read CRIS BOURONCLE/AFP via Getty Images)

Cris Bouroncle/AFP/Getty Images

Related article

Scientists present evidence supporting a potential origin story for the Great Sphinx. One reason why ancient star dunes may have been disregarded for a significant period is that their prevalence was not widely recognized until recently, according to Goudie's suggestion.

Star dunes have not been frequently seen in the stratigraphic record. This could be due to the fact that many geologists were more familiar with longitudinal dunes and barchans (crescent-shaped dunes), and not so much with star dunes, according to Goudie. Thanks to tools like Google Earth, we now have a better understanding of how widespread these features are.

Mindy Weisberger, a science writer and media producer, has contributed to various publications such as Live Science, Scientific American, and How It Works magazine.

Editor's P/S:

This article provides fascinating insights into the enigmatic world of star dunes, shedding light on their formation, age, and movement. The research presented challenges our previous understanding and highlights the importance of examining the geological record from a comprehensive perspective. It demonstrates the dynamic nature of these awe-inspiring landscapes and their potential implications for infrastructure development in desert regions.

Furthermore, the article underscores the significance of scientific advancements in unraveling mysteries of the past. By employing innovative techniques such as ground-penetrating radar and optically stimulated luminescence dating, scientists have uncovered hidden details about the age and evolution of star dunes. This study not only expands our knowledge of Earth's geological history but also serves as a testament to the ever-evolving nature of scientific discovery.