The Salar Grande dry lake bed is about 70m deep. To reach the oldest layers, we will dig into an outcrop in a quarry near camp. We will work near the bottom of a manmade feature known as The Wall, presumably exposed during the mining activity that occurred here. Carrying our equipment through the quarry is treacherous due to the uneven ground covered with salt nodules. The salt sounds thin in places and is streaked with colors reminiscent of alpine snowpack or ice on a glacier. Vultures eye us warily as we open up our cases and set up the generator. For today’s work, we will use a more powerful drill with an SDS-Max quick change tool interface and a chisel to dig down to unweathered salt at the base of The Wall.
Alfonso wants to remove about 12 inches of weathered overburden to get to the pristine beds below. This takes some muscle, because we must apply pressure to the chisel in a horizontal position in order for the percussive hammer to work properly. In addition, the chisel can plunge deep into a crack in the salt and get stuck. After working for about an hour, we begin to see large, clear halite crystals. The astrobiologists will look for tiny bubbles inside the salt, which may contain the remnants of ancient microbes. On this microscopic scale, the definition of life is somewhat more flexible than for macroorganisms, which can readily be identified as individuals. Since it is difficult, if not imposible, to track individual organisms at this scale as they rapidly multiply and mingle, the life span of these microbes can not be easily determined. What is known, however, is that the microbe colonies are very old because the crystals can be dated back to the age of the ancient lake (~2-5 million years).
As we chip around a large crystal of interest, Alfonso and Kim (SETI) sterilize their collection tools. The crystal is internally fractured and does not come out in one piece. Still, they collect the bits and place them in sterilized sample collection tubes. Then it is time to attempt collection of a core from the freshly exposed beds. The coring direction is horizontal, presenting a challenge for manual drilling because it is difficult to both support the drill and provide adequate force on the bit at the same time. The cuttings are pure white salt powder and we experience the same issues collecting cores as we did earlier in the nodules.