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Aphanitic (a = not, phaner = visible) rocks, in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth's surface. When extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. The individual crystals in an aphanitic igneous rock are ...
Atmospheric instability is a condition where the Earth's atmosphere is considered to be unstable and as a result local weather is highly variable through distance and time. [ clarification needed ] [ 1 ] Atmospheric instability encourages vertical motion, which is directly correlated to different types of weather systems and their severity.
In practice, the RBL is defined by the depth at which the viscosity of the mantle rocks drops below ~.. [5] However, mantle material is a non-Newtonian fluid, i.e. its viscosity depends also on the rate of deformation. [6] This means that the LAB can change its position as a result of changes in the stresses.
A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstable atmosphere, vertical air movements (such as in orographic lifting , where an air mass is displaced upwards as it is blown by wind up the rising slope of a mountain range) tend to become larger, resulting in turbulent ...
The use of rock has had a huge impact on the cultural and technological development of the human race. Rock has been used by humans and other hominids for at least 2.5 million years. [22] Lithic technology marks some of the oldest and continuously used technologies. The mining of rock for its metal content has been one of the most important ...
For example, an igneous rock such as basalt may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle , rocks do not remain in equilibrium and change as they encounter new environments.
About 3.4 billion years ago, nitrogen formed the major component of the then-stable "second atmosphere". The influence of the evolution of life has to be taken into account rather soon in the history of the atmosphere because hints of earliest life forms appeared as early as 3.5 billion years ago. [48]
The different metamorphic facies are defined by the mineralogical composition of a rock. When the temperature or pressure in a rock body change, the rock can cross into a different facies and some minerals become stable while others become unstable or metastable.