Astronaut's Guide To Life On Earth Ebook 21
Christian Erdmann
When did these gneisses form? Age determinations ofminerals containing radioactive elements show that granitewhich was intruded into them after they were metamorphosedand folded is more than 2.5 billion years old. Theymust, therefore, be older than that. Thus, they probablyare at least a billion years older than rocks containing thefirst faint traces of life on earth and 2 billion years olderthan the oldest rocks containing abundant fossils. Howmuch older is not known, but the gneisses are certainly54among the oldest rocks in North America and record someof the earliest events in the building of this continent.
The geologic story of the Teton country from the timethe earth was new to the present day has been summarized.What can we learn from it? We become aware that eventsrecorded in the rocks are not a chaotic jumble of randomaccidents but came in an orderly, logical succession. Wesee the majestic parade of life evolving from simple to complextypes, overcoming all natural disasters, and adaptingto ever-changing environments. We can only speculate asto the motivating force that launched this fascinating geologicand biologic venture and what the ultimate goal maybe. New facts and new ideas are added to the story eachyear, but many unknown chapters remain to be studied;these offer an irresistible, continuing challenge to inquisitiveminds, strong bodies, and restless, adventurous spirits.
Most geologic processes that developed the Tetonlandscape have been beneficial to man; a few have interferedwith his activities, cost him money, time, effort, andon occasion, his life. Postglacial faulting and tiltingalong the southern margin of Grand Teton National Parkdiverted drainage systems (such as Flat Creek, southwestof the Flat Creek fault on the south edge of the geologic map),raised hills, dropped valleys, and made steep slopesunstable. Flood-control engineers wage a never-endingstruggle to keep the Snake River from shifting to the westside of Jackson Hole as the valley tilts westward in responseto movement along the Teton fault. Each highwayinto Jackson Hole has been blocked by a landslide at onetime or another and maintenance of roads across slide areasrequires much ingenuity. We see one slide (the Gros Ventre)that blocked a river; larger slides have occurred in thepast, and more can be expected. Abundant fresh faultscarps are a constant reminder that public buildings, campgrounds,dams, and roads need to be designed to withstandthe effects of earthquakes. Some of these problems havegeologic solutions; others can be avoided or minimized asfurther study increases our understanding of this region.
Man appeared during the last one-fiftieth of an inchon our yardstick of time gone by. In this short span he hashad more impact on the earth and its inhabitants than anyother form of life. Will he use wisely the lessons of thepast as a guide while he writes his record on the yardstickof the future?
The experimental 45.4-kilogram (100-pound)Congreve incendiary rocket wasdeveloped as a siege weapon for use againstfortresses or entrenched enemy positions,although it is not known to have been usedin combat. The 6.7-meter (22-foot) guidestick screwed together and fitted to the sideof the projectile before firing. Like thesmaller Congreve rockets, it could belaunched from a frame or earthen embankment.