Deserts are treasures of paleontological findings

The world's deserts serve as a natural laboratory for investigating the history of life, be it that of plants and animals or of humankind. This is because the desert's sparse vegetative cover, lack of thick soils, and aridity combine to provide large areas of exposed rock. This, together with the scant precipitation that reduces chemical leaching by groundwater, promotes the preservation and the detection of fossils that allow deciphering the evolutionary history of animals and plants, and of early man (Figure 3.8). Although ultimately it is the distribution of appropriate aged sedimentary rocks that determines where fossils will (and will not) be discovered, deserts probably have produced a disproportionate number of major paleontological finds. Particularly noteworthy examples include the badland terrains of the Gobi Desert where a great diversity of late Cretaceous (65 million year-old) dinosaurs and mammals have been unearthed; the Sahara's Ténéré Desert in Niger where excavations in lower Cretaceous - 10 Ma (million years ago) - rocks recently recovered over 25 tons of dinosaur fossils; the Karoo Desert of South Africa and its exposures of upper Permian (250 Ma) through lower Triassic (220 Ma) rocks containing abundant remains of mammal-like therapsid reptiles; Egypt's Fayum Desert, which preserves important Eoceneage (40 Ma) fossil treasure of early cetaceans and sirenians; the Pisco Basin, a coastal desert in Peru, where an exposed stratigraphic sequence of Miocene to Pliocene (20 to 2 Ma) rocks has produced spectacular assemblages of fossil marine mammals; and the Colorado desert in southeastern California, that harbours one of the most complete records of late Cenozoic land mammal evolution in North America.

Findings in deserts shed light on the origins of mankind and its culture

Some fossils of hominids found in deserts in recent years were instrumental in reconstructing the evolution of humans. The early hominid Sahelanthropus tchadensis, a new genus and species of hominid that lived 6-7 million years ago (Vignaud and others 2002) was discovered in 2001 in the Saharan Djurab Desert of northern Chad. This finding suggests that the divergence between the human and chimpanzee lineages was earlier than indicated by most molecular studies. Australopithecus garhi, who lived 2.5 million years ago, was found in 1996-9 in the Afar Desert of Ethiopia. Australopithecus garhi might have been the world's earliest maker of stone tools, used to scrape bones of hunted mammals (Asfaw and others 1999). The oldest found fossilized remains of modern humans, who lived 160 000 years ago, was found in 1977 in the desert sands near the Ethiopian village of herto (White and others 2003). Most desert attributes that conserve fossils also apply to preservation of prehistoric and archaeological remains; and the low level of surface disturbance by humans has also preserved prehistoric sites.

These attributes have resulted in a large number of archaeological discoveries in deserts, many of which are of global significance. For example, the earliest stone plough-tips, the largest and oldest cluster of threshing floors (Figure 3.9) and the earliest run-off irrigation system supporting large cultivated fields, belonging to early farming communities which evolved from hunter-gatherers since 6 000 BCE, were found in the Negev Desert (Avner 1998). Among hundreds of prehistoric cult sites in West Asian deserts, shrines of standing stones representing deities have been found (Figure 3.10), erected first in the 12th millennium BCE and becoming very common from 6 000 BCE. These suggest that while peoples of the fertile lands of that region worshiped gods in figurative, human or animal forms, natural, unshaped stones represented gods to the desert people. Millennia later, this abstract, non-figurative theology was also adopted by the Jewish, Nabatean and Islamic religions (Avner 2000). Another rather famous desert finding with religious implications, that of the Dead Sea Scrolls, preserved for 2 000 years due to the desert's dry climate and discovered since 1947, shed new light and contributed insights into the history, philosophy and evolution of Judaism and early Christianity. Less widely known but of far-reaching impact is the desert origin of alphabetic writing, which first appeared in West Asian desert rock inscriptions around 2 000 BCE. While the ancient Egyptian and Mesopotamian scripts consisted of hundreds of complex signs (Figure 3.11), a group of people in the Sinai desert adopted only 28 (mostly Egyptian) symbols, each representing a single consonant. Later, these signs evolved into the Phoenician and the Hebrew script, then to the Greek and Latin and finally into the present-day Western European scripts.

Desert research generated knowledge on the earth's geology

The low soil and vegetation cover of deserts has also attracted geologists and geomorphologists, whose research in deserts has contributed to our basic understanding of the processes that shape and mould the surface of the earth. The wealth of excellent rock exposures in the rocky deserts is outstanding, providing scientists and visitors with a glimpse into geological windows. Deep canyons, fault escarpments and rift valleys in deserts often exhibit sequences of rock strata that disclose chapters of hundreds-of-millions of years of earth history. Deserts have also been pivotal to the development of geomorphology, largely because their landforms are also easy to see. John Wesley Powell's report on the Grand Canyon (Powell 1875) opened geological science to the power of rivers, and Gilbert's (1877) work in North American deserts, are the foundational studies of modern geomorphology.