Nature
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The sandy landscapes of southern Utah are home to a bizarre geological phenomenon. Brown-black balls ranging in size from a pea to a grapefruit litter the deserts of the Beehive State (and other parts of the southwestern United States), congregating in large formations that have stumped scientists for decades. These strange shapes, known by various names but most commonly “Moqui marbles”, have existed for millions of years.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.The name comes from the Hopi Tribe, Nature reports. According to legend, the ancestral spirits (“moqui”) of tribe members would visit Earth at night and play marbles. The spirits were gone by morning but would leave the marbles so as to let living relatives know they were happy. However, research has revealed the origins of the Moqui marbles are a little more mundane. According to the Utah Geological Survey, the balls are iron concretions composed of iron oxide and sandstone and forged in groundwater that collected underneath million-year-old rock.
The sandstone that exists in Utah and its neighboring states is a rust-like color thanks to a microscopically small layer of an iron oxide called hematite that surrounds the grains of sand. It derives from rock deposited some 190 million years ago. However, over time, other sediments covered the sand, leading to the formation of sandstone. Meanwhile, reducing agents such as acid dissolved iron into water flowing through the porous rock. It is from this groundwater that the Moqui marbles were formed.
The marbles only became visible after weathering caused the outer layers covering the sandstone to erode, revealing the sandstone underneath and the iron balls they contained. While commonly found in spherical shape – hence the name – they can occur in other formations, including pipes and UFO “flying saucers”. A study published in 2004 puts the oldest marbles at 25 million years old and found some are as young as 2 to 5 million years old.
The balls are commonly found in the US but similar structures have been discovered in other parts of the world, such as Mongolia. Perhaps most excitingly, these marble-like objects have also been found on Mars. Nicknamed Martian "blueberries" thanks to their small, gray-blue color, some scientists believe they are some of the first indications of the historical existence of water on the Red Planet. Another study noting similarities between Martian blueberries and Moqui marbles suggests they may have formed under an early carbon dioxide-rich atmosphere.
