Earth Science: Origins and Geology – Ecosystems
Animals and plants, together with the environmental conditions, soil, and climate of a place, create diverse, often sensitive ecosystems.
Only small changes in the environment are required to upset the many interdependent relationships within the system, and destroy the balance that helps different species survive.
Types Of Deserts
Deserts and semideserts cover about one-third of the Earth’s land surface. The best known desert, the Sahara, is also the largest. It extends over 3.36 million square miles (8.7 million km 2).
A desert is a hostile environment with little vegetation and commensurately sparse fauna. The lack of water prevents most plant growth in dry deserts. Such drought is usually caused by the absence of rain. For instance, if an area lies on the leeward side of mountain ranges—such as the South American Atacama Desert along the western side of the Andes, or the North American Mojave Desert, west of the Rocky Mountains—it receives little precipitation.
The Gobi desert in Central Asia exists because of a permanently dry continental climate. Passat (trade wind) deserts, such as the Australian Simpson Desert, are created by constant subtropical high-pressure belts that inhibit the penetration of moist air masses into arid regions.
Semideserts and cold deserts
In hot deserts of the tropics and subtropics, such as the giant Sahara in North Africa, the Arabic deserts, or the Chinese Taklimakan, high evaporation rates further deplete water supplies. A lack of cloud cover leads to extreme daily temperature fluctuations. Temperatures reach up to 175T (80°C) during the day as the sun heats the ground unimpeded.
During the night, the temperature drops, sometimes below freezing. In a semidesert, like the South African Kalahari Desert, at least one wet month allows plants to grow. There are also cold deserts, such as the Wright Valley in Antarctica, where the absence of suitable temperatures above the freezing point prevent the spread of vegetation.
Sand dunes and rubble fields
Although deserts are often associated with enormous sand dunes, only three percent of them are sand deserts. The largest sand desert is the Rub Al-Khali, with dunes that cover the southern third of the Arabian Peninsula. Deserts consisting of rocky rubble fields or severely weathered mountainous regions are much more common.
Gravel deserts may be formed by erosion or could be relics of glacial deposits. Salt deserts, such as the Salar de Uyuni in Bolivia or the salt flats in Utah, develop from the evaporation of salt lakes.
BASICS
DESERT LACQUER Iron and manganese oxides, oozing via capillary action from rocks, covered with clay dust and spreading out like a brownish black lacquer.
DESERT ROSE Rosette like crystallizations, from a gypsum and sand gram mixture, formed through evaporation of water in salt lakes, but also through the weathering of gravel
DESERT GLASS Developed 28 mil- lion years ago through meltdown of desert sand, due to pressure and heat from a meteorite impact, into purest glass consisting of 98% silica and traces of iridium.