Dating record hand planes

Early cores were often collected with hand augers and they are still used for short holes.A design for ice core augers was patented in 1932 and they have changed little since.Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years.Cores are drilled with hand augers (for shallow holes) or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core.The proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures, and the air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as carbon dioxide.When the sun approaches its lowest point in the sky, the temperature drops and hoar frost forms on the top layer.Buried under the snow of following years, the coarse-grained hoar frost compresses into lighter layers than the winter snow.

Ice cores have been studied since the early 20th century, and several cores were drilled as a result of the International Geophysical Year (1957–1958).Impurities in the ice provide information on the environment from when they were deposited.These include soot, ash, and other types of particle from forest fires and volcanoes; isotopes such as beryllium-10 created by cosmic rays; micrometeorites; and pollen.As further layers build up, the pressure increases, and at about 1500 m the crystal structure of the ice changes from hexagonal to cubic, allowing air molecules to move into the cubic crystals and form a clathrate.The bubbles disappear and the ice becomes more transparent.As a result, alternating bands of lighter and darker ice can be seen in an ice core.Ice cores are collected by cutting around a cylinder of ice in a way that enables it to be brought to the surface.With the aid of a tripod for lowering and raising the auger, cores up to 50 m deep can be retrieved, but the practical limit is about 30 m for engine-powered augers, and less for hand augers.Below this depth, electromechanical or thermal drills are used.The lowest layer of a glacier, called basal ice, is frequently formed of subglacial meltwater that has refrozen.It can be up to about 20 m thick, and though it has scientific value (for example, it may contain subglacial microbial populations), Cores are often drilled in areas such as Antarctica and central Greenland where the temperature is almost never warm enough to cause melting, but the summer sun can still alter the snow.

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