Some 10,000 years ago, there were believed to be many mighty rivers that flowed from the Himalayas and that allowed civilizations to prosper in the green, fertile, cool climate on the riverbanks in northwestern India, such as Rajasthan. Archaeologists have determined that ample precipitation and large flowing rivers enabled settlers to be prosperous farmers. Then, 6,000 years ago, one of the mightiest rivers, the Saraswati, dried up, forcing inhabitants in the area to relocate elsewhere.
Over time, the Saraswati River, spoken of in ancient holy writings, slowly became a folklore legend because no one could find any physical trace of it. Then, through the use of satellite imagery, scientists recently discovered evidence of a once-major river 5 miles (8 km) wide that flowed through northwestern India. They were also able to determine that it dried up 4,000 years ago—the same time the Saraswati disappeared. Both climate and geology are believed to have ultimately caused its disappearance.
Scientists using remote sensing are currently working with India's water experts to drill boreholes to seek water under the desert in the same area. Water they have retrieved so far from deep under the riverbed has been carbon dated at about 4,000 years old. More than 1,000 archaeological sites have also been discovered along the river course. Many believe this old riverbed may be the ancient Saraswati. As in Darfur, the location of groundwater from ancient water courses could help large populations in the face of drought conditions from global warming.
Scientists in the United States have used remote sensing images from around the country to identify and inventory stands of existing primeval forest. Most of these old trees are found in rugged, steep, out-of-the-way areas that are undesirable to build in, farm on, or harvest for lumber. Paleoclimatologists are extremely interested in these areas because some of the trees are thousands of years old and can provide a valuable record of droughts and floods that have occurred throughout time, enabling them to better understand environmental issues such as global warming. To date, old-growth stands have been found in the New England states, the Carolinas, Arizona, California, Texas, Nevada, Oklahoma, and Virginia. Scientists are hopeful that a better understanding of the wet and dry cycles of climate will increase their knowledge of global warming, climate change, and long-term predictions.
This image pair depicts the Safsaf Oasis in Egypt. The image on the left is produced from the LANDSAT satellite of the Earth's surface, showing very few drainagelike features. The image on the right is a radar image, depicting the subsurface rock features. The dark veinlike patterns depict ancient watercourses. (NASA/JPL)
safsaf oasis, Egypt
Visions of the Sahara today do not invoke images of major rivers and connecting multiple tributaries. Today the landscape looks like vast, open areas of nothing but sand for miles in all directions. As in the previous examples, even though the surface may not show any signs of water, this does not mean that water did not flow and cut tributaries at one time, only to later dry up and become covered with sand. At one time, abundant rivers in the Safsaf, Egypt, carved channels through canyons and formed lakes, and today these "fossil rivers" are buried under the sand.
In the photograph, the image on the left was obtained from a LANDSAT satellite. The surface looks hard and smooth, but upon close inspection one can see a very faint river channel that runs across the image. The image on the right of the same area, however, is what the subsurface of the ground looks like. This image was obtained from the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR), which uses radar to penetrate the thin sand cover on the Earth's surface, and was taken aboard the NASA space shuttle Endeavour. This image shows that the area was once very different—the oasis was once a very productive, lush river valley. The sinuous dark channels (especially on the lower left) were cut by a meandering river and its tributaries. Such evidence helps climatologists reconstruct a region's climate in order to better understand the past, present, and fUture.
central sahara, Africa
NASA acquired a moderate-resolution imaging spectroradiometer (MODIS) image of the Sahara in Africa just north of Algeria and Libya. They studied three major rock formations among the reddish sand dunes: the Tassili, Tadrart-Acacus, and Amsak. Remote sensing specialists were able to identify several ancient riverbed structures in the Acacus and Amsak regions that followed a dendritic (treelike) pattern. Paleoclimatologists have interpreted this image and determined that the area was wet during the last glacial era, covered with forests, and probably inhabited by several species of animals. In addition, several renditions of ancient rock art have been found in the area, which indicates that the area provided a home for an ancient civilization. Experts have determined that the area became extremely arid about 3000 b.c.e.
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