The two Mars exploration rovers, Spirit and Opportunity, touched down on Mars in January 2004 and have been conducting extensive observations with the Athena science payload. Together the two rovers have traversed approximately16 km. Spirit, located on the floor of Gusev crater, has investigated basaltic plains, as well as older materials in the Columbia Hills. The rocks of the Columbia Hills are largely clastic in nature and range from breccias to finely laminated deposits that have undergone significant aqueous alteration. They appear to be largely a mixture of altered impact ejecta and explosive volcanic materials. Recently, Spirit has discovered silica-rich deposits that may have formed in a hot spring or fumarole environment. Opportunity has carried out the first outcrop-scale investigation of ancient sedimentary rocks on Mars. The rocks are sandstones formed by wind and water erosion and re-deposition of fine grained siliciclastics and sulfate-rich evaporites. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed locally near the top of the section. While liquid water was present at Meridiani below and occasionally at the surface, the ancient environmental conditions recorded there are dominantly arid, acidic and oxidizing, and would have posed some significant challenges to life.

Photos by Opportunity, which spent about 300 Martian days traversing the rim of Victoria Crater, 2006-2007.

The gradual closing of the Indonesian Seaway and the onset of northern hemisphere ice ages

A logical argument can be made that the closing of the Indonesian Seaway transformed the shallow, tropical Pacific Ocean from a state resembling that during large El Niño events to its modern weakly La Niña state, and with that change, atmospheric heat transport to Canada decreased sufficiently to permit the growth of large continental ice sheets. The steady northward movement of New Guinea and the concurrent emergence of islands in the "Maritime Continent" (largely Indonesia) has blocked relatively warm Pacific water south of the equator and enabled cooler water from the northern Pacific to escape into the Indian Ocean (the "Indonesian Throughflow"). Blocking of that warm water may have strengthened easterly winds and amplified an east-west temperature gradient. Paleoceanographic evidence, indeed, shows a gradual cooling of the water in the eastern Pacific to its present-day "cold tongue" that flows at the equator half way across the eastern equatorial Pacific. Thus, the sea surface temperature of the eastern Pacific has gradually changed from the warm state that is reached only rarely today during major El Niño to its more common present-day cold state. Moreover, during present-day El Niño events, distant regional climates respond, via "teleconnections," in varying ways in response to the changes in sea-surface temperatures in the eastern Pacific.

Similarly, paleoclimates from most of the earth differ from normal present-day climates. These differences, those between paleo- and typical modern climates, resemble those associated with modern teleconnections, which corroborates the idea that before ~3 Ma, the tropical Pacific Ocean was in a state similar to that during El Niño events. For example, during El Niño events, not only do winters in Canada become atypically warm, but also summers last longer than normal. An assessment of the dependence of positive-degree days in Canada associated with El Niño events, together with empirical estimates of melting rates of snow or ice as a function of positive-degree days, suggests that an eastern Pacific 3- 4 degrees C warmer than today, as it was at 3-4 Ma, sufficed to melt winter snowfall and prevent ice sheets from growing. The gradual cooling of the eastern Pacific and reduced atmospheric heat transport finally enabled ice sheets to grow.

April 2008

We’ll meet at 8 a.m. at the Cold Spring RTD Park-and-Ride on Union Blvd just south of 6th Avenue in Lakewood. Travel will be by car-pooling; those who live along US-285 can also meet us at approximately 8:30 a.m. at the Twin Forks Park-and-Ride, located on the south side of US-285 about ½ mile west of the Indian Hills (Parmalee Gulch) turnoff and just past South Turkey Creek Road. We’ll be driving to Harris Park, located about 6 miles north of US-285 from Crow Hill, and then on Forest Service dirt roads about 2 miles to the site, a total of about 45 miles from Lakewood.

We will be able to hunt in the granite pegmatites for smoky quartz, microcline var. amazonite, and if one is fortunate, goethite, fluorite, and topaz. Pete will brief the group about the geology of the pegmatites and the minerals found in them. The area is pleasant, lightly wooded with a small stream, and is kid-friendly. The site is on mining claims maintained by the Littleton Gem and Mineral Club, and we will be there courtesy of that club. Depending on how industrious you want to be in searching for or digging for minerals (the best are found down in the undisturbed soil or bedrock, you know), bring any or all of a rock pick, trowel, chisel, sledge, a small or large shovel, and pickaxe. Safety glasses or goggles are advised if splitting rocks, as well as suitable sun/rain/snow protection depending on the weather. You will also be required to bring your own lunch, drinks, and snacks. There will be no charge for this trip.

May 2008

By Charles E. Chapin, New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and TechnologyBy Technology

December 2008