EVA: EVA to Candor Chasma and Stacy's Cake took additional soil samples. White, orange, and black colored lichen were discovered on a boulder some hundred meters west of the head of the canyon below Stacy's Cake-While it's a bit optimistic to hope that we will find such lichen on the Martian surface, we will definitely search for similar organisms within rocks or deep underground.

LSS: The Nov. 19th sample from the interior grey-water tap is covered by a diffuse off-white film, indicating the absence of dye-activating coliforms, while the Tank 5 sample is very nearly as colorless. Compared against a white background, it is a darker grey with no noticeable coloration. This is a bit odd, since one would expect high coliform content in the Tank 5 sample. In case they have not been kept warm enough, I am placing them in the newly discovered incubator (donated last season by Princeton), although there is a high risk for contamination by slower growing non-coliforms.

Labwork: I finally got to work looking at our supposed endoliths compared to nearby soil controls, and it looks good for us having found endoliths. Here's the skinny:

• The grey sandstone (Sample 11-19a) collected Nov. 19th from the head of the canyon beneath Stacy's Cake was confirmed to have spheroidal microorganisms similar to those examined and discussed in the Nov. 18th report. Short branching chains and clusters of several dozen spheres were apparent. This is a good validation of the macroscopic sample collection method, in that the grey sandstone was sampled because it had brown encrustations on its interior fractures largely identical to those of samples 11-18g and h.
  
  
• Next I examined a sample of dry stream bed material directly upstream of the grey sandstone 11-19a. This was to act as a control, to see if the suspected endolithic organism was also present in non-endolithic environments, and therefore not actually an endolith but more likely contamination, or, even worse, a trick of the microscope optics. Now, before I go on, I should say that this evaluation when done more seriously should be done blind-That is, I shouldn't know whether I am looking at boring old streambed sand in which I don't "want" to find my suspected endolith, or endolithic scrapings in which I do, since, like all scientists, I want to make a big (or, in this case, at least interesting) discovery, and such knowledge could very easily bias my findings. Accepting that caveat for the moment, it appears that the suspected microorganisms that are more or less ubiquitous amongst the particles scraped from the endolith sample are largely absent in the dry surface sand. Many times I found structures similar to the suspect microorganisms of 11-19a, but these generally were ruled out as optical effects as I moved the focal plane through the entire particle, and even when I could not rule out the possibility of similar microorganisms in this surface sand, the shapes, their uniformity, and relations with each other were not nearly as compelling an argument for an in-place living population as with endolithic sample 11-19a.
  
  
• Sample 11-21a consisted of a mixture of wet sand and mud directly downstream from sample 11-19a. It was difficult to evaluate 11-21a because the due to the moisture of the sample the slide was much less "clean," in that instead of just a few isolated particles of substantial size there was a wide scattering of particles similar in size to the tiny spheres that were the object of this search. Nonetheless, when focusing the search on the periphery of the larger crystals within 11-21a, no suspected microorganisms were found.

Looking at the past three samples, it can be reasonably argued that the tiny spheres within sample 11-19a are indeed an indigenous endolithic microorganism-We found life on Mars! The next step would be to take the endolith samples back to Earth (aka the Nealson Lab at USC) and see if we can ampliy and sequence certain DNA strands within the suspected microbes, and use these to identify the organism(s). Now, on Mars, any extant life we might find could easily fall beyond the reach of such a conventional approach-It might not even have DNA! But we'll cross that bridge when we come to it. In the meantime, we can be satisfied that a crew doing analogue research in a simulated Mars base can make some real discoveries-Who knows what a real Mars crew could do?

Now, to wrap up a few of the other samples collected on the 19th:

• 11-19c was a red sandstone sampled for several splotches of orange brown crust on its surface. Under the stereoscope, appearance was mineralogical, but at 800x particles scraped from the splotches had potential cellular structures associated with their surfaces. However, scrapings from the regular surface of the rock had similar features, and the irregularity of the structures with relation to each other and their heterogeneity of size leaves me skeptical as to their biogenicity. More investigation required.
  
  
• 11-19d was a very interesting suspected hypolithic mat material taken from beneath a conglomerate on the cliff-side of Stacy's Cake. However, the mat did not seem to be in place, and I can now explain it thanks to the lichens we found today, the 21st. Under the microscope, sample 11-19d appears to be some black lichen material that somehow got under the rock-Perhaps sometime in the past the lichen were growing on the upper surface of the rock, and then the rock tumbled over, preserving the lichen.