8 Moqui Marbles

When geologists and collectors began to explore the Navajo Sandstone of southern Utah, they sometimes came across vast numbers of very hard, iron-rich concretions. Their size ranged from about 1 mm to as large as 4 inches but most were of approximate marble size; what better name to call them than “Moki marbles;” Moki, or Moqui, was the name then used for the Hopi Indians. For years they were commonly found and could be purchased at rock shops throughout the Southwest.

Dr. Marjorie Chan is a research scientist at the University of Utah with a particular interest in concretions and especially those from southern Utah. She knew that Utah concretions most likely formed when briny fluids encountered oxygen-rich groundwater. Under these conditions iron-rich minerals precipitate and cement with sand grains to form the mostly hematite marbles. Key to their formation is the requirement that water be present to enable the process to occur.

Unexpectedly, Dr. Chan’s work has recently become closely connected with the exploration and scientific investigation of the planet Mars. It was the possibility of finding primitive life-forms that jump-started Martian research during the last decade of the 20th century. It began with satellite images that gave tantalizing evidence of stream channels and other evidence of water induced erosion. If there was water, could there also be life? The question on everyone’s mind was how long did that water exist before boiling off into the thin Martian atmosphere?

For life to exist, at least life as we know it, you need standing water; you need lakes and rivers and enough water to fill the atmosphere and create enough pressure to keep the water in a liquid state; you also need enough atmospheric water vapor to create sufficient greenhouse warming to keep the lakes and rivers from freezing solid. Obviously those conditions don’t exist today - but did they exist in the past?

In January 2004, an alien spacecraft from Earth roared through that thin Martian air and crash-landed on Meridiani Planum. Protected by airbags, it unfolded and a surface rover named Opportunity, rolled down a ramp and began six years of exploration; it is still in operation today. One of its first discoveries at Meridiani were many small iron-rich pebbles which the JPL and NASA people have named “Blueberries”; they look blue when contrasted with the red Martian soil. Dr. Chan was elated. She knew they had to be the same or very similar to the Utah concretions which she had been studying. She was right; the Blueberries, like the Moki marbles, were rich in course-grained hematite. In the same location Opportunity discovered shore-lines, consistent with wave action from an ancient Martian lake. Here was proof that standing water had once existed on Mars.


Some information for this essay comes from an article published in a Grand Staircase Escalante National Monument news article written by Dr. Marjorie Chan and also from an article from Sky & Telescope Magazine, July, 2009, Uncovering Mars’s Secret Past, by Jim Bell.