On Earth, we know skipping stones don’t end up on a shore or beach by accident. It’s Mother Nature who places them there after a long and bumpy journey that could take millions of years and cover hundreds of miles. Part of the reason we know this is because skipping stones don’t start out looking and feeling like skipping stones. They begin their life like most other rocks, jagged shards of material somehow sheared away from the Earth’s crust by the movement of tectonic plates or by erosion. The difference is, they are exposed to a moving fluid for an extended period of time.

During its water-propelled journey here on Earth, our rock is pummeled by particles and thrown into obstructions only to be pushed farther along by the force of water. Each impact it endures, however minute, leaves its mark. Many years later, the rock has been transformed into the smooth-surfaced creation that begs to be flung at a low angle across the water. In the geology world this process is known as abrasion.

So when we see rounded rocks on Mars we know that at that location a river ran through it, at some point in its history. From the size and the shapes of the mixture of stones found together come clues to the speed of the water flow and the distance that the stones have traveled to reach their present location. Working the data we have received so far, we believe the water source that propelled our skipping stone to its present location was anywhere from ankle to hip-deep and flowed at about 3 feet per second. The distance traveled and the source of the water is unknown, but in my mind’s eye I can picture the different scenarios that could bring that little stone into existence. And to a planetary geologist, each and every one of them has its own inner and outer beauty. Perhaps one day, our insatiable Curiosity will help us learn which of these scenarios is correct.

In the meantime, we’ve put our skipping stones in the rover’s rearview mirror (several of our 17 cameras watched them disappear over the horizon) and moved forward in both time and space.

Just the other day, we crossed another significant threshold of the mission by processing our first sample of Mars in one of Curiosity’s onboard chemistry labs. Essentially, we’re eating dirt and loving it. With this step, we’ve begun doing the kind of exacting scientific research you would usually only be able to accomplish in a fully stocked laboratory at a university or research center. Now, we’re doing it on Mars.