Meanwhile on Mars: "This rock is made up of rounded gravels in a matrix that's very sand rich," Rebecca Williams of the Planetary Science Institute in Tucson, AZ, told reporters. "And these attributes are consistent with a common sedimentary rock type called a conglomerate. ... Over time, erosion is working on that rock face and liberating some of the gravels and they're falling down and accumulating in a pile at the base of that outcrop."