Scientific Research

Carbon cycle

One of the major cycles of chemical elements in the environment is carbon cycle. Carbon (as carbon dioxide) is taken up from the atmosphere and incorporated into the tissues of plants in 'photosynthesis. It may then pass into the bodies of animals as the plants are eaten. During the respiration of plants, animals, and organisms that bring about decomposition, carbon dioxide is returned to the atmosphere. The combustion offossil fuels (e.g. coal and peat) also releases carbon dioxide into the atmosphere.

In physics it is a series of nuclear reactions in which four hydrogen nuclei combine to form a helium nucleus with the liberation of energy, two positrons, and two neutrinos. The process is believed to be the source of energy in many stars and to take place in six stages. In this series carbon-12 acts as if it were a catalyst, being reformed at the end of the series.

Carbon dating

Carbon dating (radiocarbon dating) is a method of estimating the ages of archaeological specimens of biological origin. As a result of cosmic radiation a small number of atmospheric nitrogen nuclei are continuously being transformed by neutron bombardment into radioactive nuclei of carbon-14;

14/7N + n ® 14/6C + p.

Some of these radiocarbon atoms find their way into living trees and other plants in the form of carbon dioxide, as a result of photosynthesis. When the tree is cut down photosynthesis stops and the ratio of radiocarbon atoms to stable carbon atoms begins to fall as the radiocarbon decays. The ratio ¹⁴C/¹²C in the specimen can be measured and enables the time that has elapsed since the tree was cut down to be calculated. The method has been shown to give consistent results for specimens up to some 40 000 years old, though its accuracy depends upon assumptions concerning the past intensity of the cosmic radiation. The technique was developed by Willard F. Libby and his coworkers in 1946-47.

Acid rain

Acid rain is precipitation having a pH value of less than about 5.0, which has adverse effects on the fauna and flora on which it falls. Rainwater typically has a pH value of 5.6, due to the presence of dissolved carbon dioxide (forming carbonic acid). Acid rain results from the emission into the atmosphere of various pollutant gases, in particular sulphur dioxide and various oxides of nitrogen, which originate from the burning of fossil fuels and from car exhaust fumes, respectively. These gases dissolve in atmospheric water to form sulphuric and nitric acids in rain, snow or hail (wet deposition). Alternatively, the pollutants are deposited as gases or minute particles (dry deposition). Both types of acid deposition affect plant growth - by damaging the leaves and impairing photosynthesis and by increasing the acidity of the soil, which results in the leaching of essential nutrients. This acid pollution of the soil also leads to acidification of water draining from the soil into lakes and rivers, which become unable to support fish life. Lichens are particularly sensitive to changes in pH and can be used as indicators of acid pollution.

<== попередня сторінка	\|	наступна сторінка ==>
The rusting of metals	\|	Alloys and types of alloys

Не знайшли потрібну інформацію? Скористайтесь пошуком google:

Генерація сторінки за: 0.001 сек.