Tag Archives: everton formation

Geopic of the week: Stromatolites


Pictured here are the fossil remains of the first living organisms known to ever flourish on earth: the stromatolites.  They were not giant, ugly mushrooms, as you might expect from this picture.  They were in fact, structures built by microbes, and made of sediment they trapped in their secretions.

Stromatolites are formed by colonies of marine bacteria or algae.  They build the stromatolites up into mounds, like the one above, by secreting a layer at a time.  The algae and bacteria are shallow water critters that absorb their energy from the sun and don’t require oxygen, thus they were able to thrive in the oxygen free atmosphere of early earth.  Though they lived more than 2.7 billion years ago, they still exist today, but they aren’t abundant anymore.

This stromatolite fossil was collected in northern Arkansas from the Ordovician Everton Formation, and is about 450 million years old.

For more views of stromatolites, click here

Geopic of the week: Dye tracing


Dye tracing is a tool commonly used by geologists to monitor how water moves through the ground.  The above picture is from a study the Arkansas Geological Survey conducted for local residents  in Izard County, Arkansas.  Dye was added to water to track the path of farm runoff entering the groundwater through a sinkhole.

The test consists of pouring brightly colored, non-toxic dye into water before it enters the ground.  Charcoal packets, capable of detecting low concentrations of the dye, are placed in nearby springs and wells.  After some time has passed, the packets are analyzed to see where the water and dye travelled after soaking into the ground.

Because the earth is often their laboratory, geoscientists have to come up with creative approaches to studying inaccessible places.   Besides, there’s just something satisfying about dyeing large quantities of water bright colors.