Limestone, calcium-41 dating

The process for making calcium oxide is believed to be one of the first chemical reactions known to humans, dating back to prehistoric times. When limestone (calcium carbonate CaC03) is heated, carbon dioxide (C02) is driven off, leaving calcium oxide behind. The reaction was probably discovered very early in human history because limestone is a common, readily available material in the form of chalk and sea shells, and the amount of heat needed to produce the reaction can easily be produced in a simple wood fire. A more efficient method for carrying out the reaction is to heat the limestone in a kiln (oven) at temperatures of 5oo°C to ° (900°F to i,6oo°F), resulting in a more complete conversion of calcium carbonate to calcium oxide. This method is still used today for the commercial preparation of calcium oxide. 

Calcium oxide dates from prehistoric times. It is produced by heating limestone to drive off carbon dioxide in a process called calcination CaCO , —-—> CaO, + CO ,At tem-peratures of several hundred degrees Celsius, the reaction is reversible and calcium oxide will react with atmospheric carbon dioxide to produce calcium carbonate. Efficient calcium oxide production is favored at temperatures in excess of 1,000°C. In prehistoric times limestone was heated in open fires to produce lime. Over time, lined pits and kilns were used to produce lime. Brick lime kilns were extensively built starting in the 17th century and the technology to produce lime has remained relatively constant since then. 

Electrons become trapped in the crystal lattice of minerals from adjacent radioactive material and alter the magnetic field of the mineral at a known rate. This technique is used for dating bone and shell, since it does not destroy the material, such as carbonates (calcium) in limestone, coral, egg shells, and teeth, by exposing it to different magnetic fields. 

Rule 6 addresses compounds that contain the carbonate ion— CO3. Some of the most common minerals in nature are various forms of calcium carbonate (CaCOj) and include calcite, Umestone, aragonite, travertine, chalk, and marble, all of which are white in color. Some limestone consists of very large formations that are now exposed to view. The famed white cliffs of Dover, England a large layer of the Grand Canyon in Arizona and an exposed layer of limestone in the Guadalupe Mountains of Texas, which date from the Permian Era, are all made of calcium carbonate. 

The machine SorTech has developed uses a rotating conical bowl with a cone angle, surface roughness and rotational speed calculated to best suit the particular classification requirement. The machine concept is based on the observation that for particles sliding over a surface of roughness comparable to the particle size, the apparent friction coefficient depends on the particle size. The complete machine is fully enclosed, has a small footprint and a very modest power requirement, and depending on size can process powder at the rate of kilograms to tons per hour. To date, classification has been obtained with several different metal spheroidal particles, coal powder, crushed limestone, fly ash, calcium carbonate and other powders. 

Among these only the lumps belonging to the latter group are suitable for radiocarbon dating. Over-burned pieces of lime contain sintered calcium oxide which is less reactive with water (Elsen, 2006). Consequently, if carbon is contained within these samples, it must not be considered representative of the atmospheric carbon dioxide at the time of the building process. Unburned pieces of limestone contain carbon dioxide of geological origin, while calcium contained inside the lumps of silica is mainly bonded to the silicon rather than to the carbon dioxide (Bakolas et al., 1995). Problem connected to the concretions have already been discussed previously (par. 2.2)... 

---