Carboniferous
46
Carboniferous -tgeological time scale.
carbon, organic virtually all chemical compounds with the reduced C atom
(valence -4) as major constituent. Molecules almost always also contain R,
0, as well as sometimes N, P, S, and also trace amounts of other elements. On
earth virtually all these have been formed on the basis of photosynthesis, that
is the conversion of COz by plants (on land) as well as algae (in the sea) with
the required energy provided by sunlight. Exceptions are submarine hydrothermal ecosystems which are supported by geothermal energy. All living
biota, whether plants, animals, or bacteria consist of organic compounds
(e.g., carbohydrates, proteins, lipids) and are the natural precursors of
"dead" organic carbon. The latter may be dissolved organic carbon (DOC) in
seawater (including large complex humic and fulvic acids), organic carbon
stored in marine sediments including petroleum, natural gas (methane), as
well as organic carbon in soils on land, which may finally become preserved
as peat or coal. Living organic carbon consists predominantly of chains of C
atoms (aliphatic molecules), whereas dead natural organic carbon may contain relatively more C-rings (aromatic molecules). For centuries it was
believed that organic carbon compounds can only be formed by organisms,
yet from 1783 (potassium cyanide by Scheele) onwards (e.g., ureum by
Wohler in 1828, later more complex compounds by Berthelot), organic synthesis has evolved rapidly in the laboratory as well as in manufacturing. This
has led to the introduction of many new organic compounds in the marine
environment, including the generally toxic classes of halogenated (chlorinated, brominated) organics. -tcarbon cycle.
carbon, radioactive due to cosmic radiation, a number of natural radionuclides are
formed in the atmosphere. Radioactive carbon such as 14C is formed due to
neutron capture by nitrogen, whereby stable 14N is transformed into 14C. The
approximate rate is 1.8-2.5 atoms cm- z S-I. 14C has a half-life of 5730 ± 40
years, and is therefore used as a tool to determine the age of organic material formed up until 40000 years ago, on the basis of its 14C/1ZC ratio.
Because, however, many radiocarbon dates have been published which are
based on the old half-life of 5568 years, this value is still used conventionally. In oceanography, 14C has been widely applied to determine the age of
water masses by the isotope ratio of dissolved total COz' and is subsequently an estimate of deep-sea circulation patterns of major ocean basins. 14C age
determinations have as interferences the twofold addition of 14C derived
from bomb-test nuclear explosions from 1945 until 1963, and COz containing no 14C from fossil fuel combustion. -tradioisotopes.
Carnegie Expeditions (1909-1929) in this period a sea-going nonmagnetic observatory (no iron) constructed for the Carnegie Institution in Washington carried out seven cruises all around the world between 80 ON and 60 oS to study
46
Carboniferous -tgeological time scale.
carbon, organic virtually all chemical compounds with the reduced C atom
(valence -4) as major constituent. Molecules almost always also contain R,
0, as well as sometimes N, P, S, and also trace amounts of other elements. On
earth virtually all these have been formed on the basis of photosynthesis, that
is the conversion of COz by plants (on land) as well as algae (in the sea) with
the required energy provided by sunlight. Exceptions are submarine hydrothermal ecosystems which are supported by geothermal energy. All living
biota, whether plants, animals, or bacteria consist of organic compounds
(e.g., carbohydrates, proteins, lipids) and are the natural precursors of
"dead" organic carbon. The latter may be dissolved organic carbon (DOC) in
seawater (including large complex humic and fulvic acids), organic carbon
stored in marine sediments including petroleum, natural gas (methane), as
well as organic carbon in soils on land, which may finally become preserved
as peat or coal. Living organic carbon consists predominantly of chains of C
atoms (aliphatic molecules), whereas dead natural organic carbon may contain relatively more C-rings (aromatic molecules). For centuries it was
believed that organic carbon compounds can only be formed by organisms,
yet from 1783 (potassium cyanide by Scheele) onwards (e.g., ureum by
Wohler in 1828, later more complex compounds by Berthelot), organic synthesis has evolved rapidly in the laboratory as well as in manufacturing. This
has led to the introduction of many new organic compounds in the marine
environment, including the generally toxic classes of halogenated (chlorinated, brominated) organics. -tcarbon cycle.
carbon, radioactive due to cosmic radiation, a number of natural radionuclides are
formed in the atmosphere. Radioactive carbon such as 14C is formed due to
neutron capture by nitrogen, whereby stable 14N is transformed into 14C. The
approximate rate is 1.8-2.5 atoms cm- z S-I. 14C has a half-life of 5730 ± 40
years, and is therefore used as a tool to determine the age of organic material formed up until 40000 years ago, on the basis of its 14C/1ZC ratio.
Because, however, many radiocarbon dates have been published which are
based on the old half-life of 5568 years, this value is still used conventionally. In oceanography, 14C has been widely applied to determine the age of
water masses by the isotope ratio of dissolved total COz' and is subsequently an estimate of deep-sea circulation patterns of major ocean basins. 14C age
determinations have as interferences the twofold addition of 14C derived
from bomb-test nuclear explosions from 1945 until 1963, and COz containing no 14C from fossil fuel combustion. -tradioisotopes.
Carnegie Expeditions (1909-1929) in this period a sea-going nonmagnetic observatory (no iron) constructed for the Carnegie Institution in Washington carried out seven cruises all around the world between 80 ON and 60 oS to study