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Other seasonal markers may include dust; certain regions have seasonal dust storms and therefore can be used to count individual years.Dust concentrations may be high enough to be visible in the ice.

They are used for decoration in parks and gardens all over the world.Ice core records provide the most direct and detailed way to investigate past climate and atmospheric conditions.Snowfall that collects on glaciers each year captures atmospheric concentrations of dust, sea-salts, ash, gas bubbles and human pollutants. Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric carbon dioxide levels, and climate stability over the last 10,000 years. This picture shows a traversing field camp from December 2010. From top to bottom: * Levels of carbon dioxide (CO2). High rates of snow accumulation provide excellent time resolution, and bubbles in the ice core preserve actual samples of the world’s ancient atmosphere[6]. They come in all shapes and sizes from the smallest saplings up to the colossal redwoods of North America - it could be said that we take them for granted, yet they are vital to teaching us about many aspects of our past. Before then, tree ancestors may have looked slightly tree-like but they were not trees in any proper sense.

The dawn of the age of true trees came with the evolution of wood in the late Devonian period.

They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time[1].

Slow ice flow at the centre of these ice sheets (near the ice divide) means that the stratigraphy of the snow and ice is preserved.

Ice cores provide excellent seasonal markers allowing very accurate dating.

Seasonal markers such as stable isotope ratios of water vary depending on temperature and can reveal warmer and colder periods of the year.

420,000 years of ice core data from Vostok, Antarctica research station. From bottom to top: * Solar variation at 65°N due to en: Milankovitch cycles (connected to 18O). They spent two nights at each site, first collecting radar data and secondly collecting a 15 m shallow ice core. This schematic cross section of an ice sheet shows an ideal drilling site at the centre of the polar plateau near the ice divide, with ice flowing away from the ice divide in all direction. The large Greenland and Antarctic ice sheets have huge, high plateaux where snow accumulates in an ordered fashion.