Yellowknife Bay, Mars
Yellowknife Bay is a geologic formation in Gale Crater on the planet Mars. NASA's Mars Science Laboratory Rover, nicknamed Curiosity, arrived at the low lying depression on December 17, 2012, 125 sols, or martian days, into its 668 sol planned mission on the planet. The primary mission goal of the Mars Science Laboratory was to assess the planets potential habitability and whether or not the Martian environment is or has ever been capable of supporting life. The site was chosen after much study of the region by previous missions. The Mars Reconnaissance Orbiter observed morphological features created by the presence of liquid water, suggesting the presence of an ancient lake which could have sustained microbial life. The depression takes its name from the city Yellowknife, capital of the Canadian Northwest Territory, in honor of the 4 billion year old rock in the region surrounding the city, which matches the approximate age of the uncovered rock in Gale Crater.
Yellowknife Bay is a 5-meter depression located in the large impact crater known as Gale Crater. The Crater is located on Mars near the northwestern part of the Aeolis quadrangle just south of the planet's equator. The massive crater's central feature is a 5 kilometer mountain called Aeolis Mons, nicknamed Mount Sharp. Geologic units in the interior of the crater offer a wide range of relative ages of the impact and provide a detailed geologic history of activities within the crater.
Gale Crater is the landing site of the Mars Science Laboratory rover, which was launched from Cape Canaveral on November 26, 2011 and landed at the site designated Bradbury Landing on August 6, 2012. The rover is equipped with a more advanced suite of instruments than has ever landed on an extraterrestrial planet, perfect for assessing the geology of the target regions. From its landing point, Curiosity drove half a kilometer northeast to the low lying depression. A flatter and more lightly colored region than the previous terrain. This region was designated Yellowknife Bay. A top mission priority for the Mars Science Laboratory team was to capture a 360 degree, HD, color panoramic photo at this region. This photo was then used to select the drilling locations of the rock samples, John Klein and Cumberland, taken from Yellowknife Bay.
Conditions on Mars during the first billion years were dramatically different from present day. Whether or not the conditions were once habitable depends largely on the volatile content, specifically water(H20) and carbon dioxide (CO2), of the surface. The greatest source of evidence for the presence of these volatiles comes from observations of surface morphologies. Previous observations of Gale Crater show strata exposed at Yellowknife Bay are most likely fan or down slope equivalents such as lacustrine deposits. Curiosity used its ChemCam and Mastcam instruments to analyse the chemistry and layering of an geological outcrop designated as "Shaler". This geologic formation displayed cross-bedding features, clear indicators of past interactions with water flows. Yellowknife Bay was chosen by the Mars Science Laboratory team as the first major site for exploration, because the exposed strata was inferred to be a shallow fluvial-lacustrine deposit. These aqueous environments are believed to preserve evidence of Paleo-habitability and potentially earth-like micro organisms capable of breaking down rocks and minerals for energy, known as chemolithoautotrophs.
Until Curiosity had arrived on Mars, all surface age dating of Mars had been through relative techniques using geomorphology and crater counting methods in order to determine an estimated age of the rock layering. The Mars Science Laboratory team used the rover to collect samples from the mudstone at Yellowknife bay, then using mass spectrometer from the Sample Analysis at Mars (SAM) instrument package they measured isotopes Argon for an absolute radiometric date of the rock member, and an approximate age to its exposure to the surface.  The age of the lake bed rock was dated to 4 billion years old, and exposed by wind erosion between 30 and 110 million years ago, giving us the first absolute age of a rock on another planet.  Still, a more ideal location to search for evidence of life on Mars would have been a member exposed more recently, as few as million years or less, so it could have been better preserved from the harsh surface radiation. 
Yellowknife Bay Geology
The primary composition of most terrestrial bodies in our solar system is igneous rock, but it has long been speculated that sedimentary rock exists in great quantity on Mars, as it does on Earth.  The Curiosity rover has confirmed the presence of sedimentary rock composed of fine-, medium-, and coarse-grained sandstone basalt. This exposure is ~5.2 m thick and is divided into three unique strata. From bottom to top, these strata have been designated: the Sheepbed member (>1.5 m thick), Gillespie Lake member(~2.0 m thick), and Glenelg members (~1.7 m thick); the assemblage of members is known as the Yellowknife Bay formation.
Active erosion, attributed to both aeolain and fluvial events, has caused the Gillespie Lake Member to become weathered away, revealing the underlying Sheepbed layer and created a topographic step observable in HiRise images from the Mars Reconnaissance Orbiter. The Gillespie Lake bed appears massive and is composed of poorly sorted, angular to well-rounded grains, which make up sheetlike sandstone basalt. These characteristics further support a model of fluvial transport and deposition.
It was from the Sheepbed layer Curiosity took two drilling samples from the mudstone sedimentary rock. These drill samples were named John Klein and Cumberland and were respectfully the second and third drilling samples Curiosity retrieved from the martian regolith. The first being an eolian[disambiguation needed] deposit, named Rocknest, sampled from an area 60 meters to the west of the Yellowknife bay. The two samples were drilled 3 meters apart and within 10 centimeters of the same stratigraphic level.
John Klein and Cumberland Samples
A number of different instruments were used by Mars Science Laboratory Curiosity Rover in attempted to assess the mineralogy of the mudstone sampled from Sheepbed strata. The CheMin XRD, Mastcam, Chemcam, Curiosity's alpha particle x-ray spectrometer (APXS), and the Mars Hand Lens Imager (MAHLI) were all used in order to obtain the most complete picture possible of the chemistry and mineralogy of the two samples, which were used to infer for the region as a whole.
A large amount of phyllosilicates, clay minerals such as smectite, were found to be major constituents the two samples. Clay minerals are hydrous aluminum phyllosillicates and form only in the presence of water, further supporting the claim that an ancient crater lake once existed in this region. Other silicates were detected as well, such as the Magnesium-rich end-member of olivine called forsterite, pigeonite, plagioclase, augite, clinopyroxene, and orthopyroxene. These minerals detected are all indicative of a potential mafic source for the origin of the deposition.
After Yellowknife Bay
With the Mars Science Laboratory's primary goal of establishing whether a habitable pale-environment could have existed on Mars quickly accomplished while within Yellowknife Bay, the team of NASA scientists then directed Curiosity out of the Yellowknife bay formation and toward the original destination of Mount Sharp, which rises an impressive 3.4 miles from the base of Gale Crater. On July 4, 2013 Curiosity drove away from the Glenelg member and began its 5 mile journey to Mount Sharp. NASA scientists estimate this drive could take the rover as long as a year to complete. It will be well into 2014 before Curiosity reaches its next science destination.
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