The use of fire as a tool to manipulate the environment has been instrumental in the human conquest of Earth, the first evidence of the use of fires by early hominids dating back to 1–1.5 million years ago [1]. Even today, most human-ignited vegetation fires take place on the African continent, and its widespread, frequently burned savannas bear ample witness to this. Although natural fires can occur even in tropical forest regions [2, 3], the extent of fires has greatly expanded on all continents with the arrival of Homo sapiens. Measurements of charcoal in dated sediment cores have shown clear correlations between the rate of burning and human settlement [4]. Pollen records show a shift with human settlement from pyrophobic vegetation to pyrotolerant and pyrophilic species, testimony to the large ecological impact of human-induced fires.

https://science.sciencemag.org/content/sci/250/4988/1669.full.pdf

Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and Biogeochemical Cycles

Methane is the most abundant organic chemical in Earth's atmosphere, and its concentration is increasing with time, as a variety of independent measurements have shown. Photochemical reactions oxidize methane in the atmosphere; through these reactions, methane exerts strong influence over the chemistry of the troposphere and the stratosphere and many species including ozone, hydroxyl radicals, and carbon monoxide. Also, through its infrared absorption spectrum, methane is an important greenhouse gas in the climate system. We describe and enumerate key roles and reactions. Then we focus on two kinds of methane production: microbial and thermogenic. Microbial methanogenesis is described, and key organisms and substrates are identified along with their properties and habitats. Microbial methane oxidation limits the release of methane from certain methanogenic areas. Both aerobic and anaerobic oxidation are described here along with methods to measure rates of methane production and oxidation experimentally. Indicators of the origin of methane, including C and H isotopes, are reviewed. We identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time. From these constraints and other data on sources and sinks we construct a list of sources and sinks, identities, and sizes. The quasi-steady state (defined in the text) annual source (or sink) totals about 310(±60) × 1012 mol (500(±95) × 1012 g), but there are many remaining uncertainties in source and sink sizes and several types of data that could lead to stronger constraints and revised estimates in the future. It is particularly difficult to identify enough sources of radiocarbon-free methane.

/pdf/biogeochemical-aspects-of-atmospheric-methane-1j0pgr75la.pdf

Biogeochemical aspects of atmospheric methane

https://iopscience.iop.org/article/10.1088/0034-4885/18/1/301/pdf

The Displacement of Atoms in Solids by Radiation

The isotopic composition of reduced organic carbon

The geographic and seasonal emission distributions of the major sources and sinks of atmospheric methane were compiled using methane flux measurements and energy and agricultural statistics in conjunction with global digital data bases of land surface characteristics and anthropogenic activities. Chemical destruction of methane in the atmosphere was calculated using three-dimensional OH fields every 5 days taken from Spivakovsky et al. (1990a, b). The signatures of each of the sources and sinks in the atmosphere were simulated using a global three-dimensional tracer transport model. Candidate methane budget scenarios were constructed according to mass balance of methane and its carbon isotopes. The verisimilitude of the scenarios was tested by their ability to reproduce the meridional gradient and seasonal variations of methane observed in the atmosphere. Constraints imposed by all the atmospheric observations are satisfied simultaneously by several budget scenarios. A preferred budget comprises annual destruction rates of 450 Tg by OH oxidation and 10 Tg by soil absorption and annual emissions of 80 Tg from fossil sources, 80 Tg from domestic animals, and 35 Tg from wetlands and tundra poleward of 50°N. Emissions from landfills, tropical swamps, rice fields, biomass burning, and termites total 295 Tg; however, the individual contributions of these terms cannot be determined uniquely because of the lack of measurements of direct fluxes and of atmospheric methane variations in regions where these sources are concentrated.

/pdf/three-dimensional-model-synthesis-of-the-global-methane-lwoiox228k.pdf

Three‐dimensional model synthesis of the global methane cycle

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH(4) in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent (13)CH(4) enrichment, although other factors may also contribute.

https://science.sciencemag.org/content/sci/242/4885/1535.full.pdf

The Isotopic Composition of Methane in Polar Ice Cores

Decay Properties of Plutonium-244, and Comments on its Existence in Nature

The predicted flux on the earth of solar neutrinos has eluded detection, confounding current ideas of solar energy production by nuclear fusion. The dominant low-energy component of that flux can be detected by mass-spectrometric assay of the induced tiny concentration of 1.6 x 10(7) year lead-205 in old thallium minerals. Comments are solicited from those in all relevant disciplines.

https://science.sciencemag.org/content/sci/193/4258/1117.full.pdf

Solar neutrinos: proposal for a new test.

Nuclear constants of nine transplutonium nuclides

The isotopes of curium, berkelium and californium found in the thermonuclear debris of the November 1952 thermonuclear test are discussed. The instantaneous buildup of the heavy elements in the thermonuclear device is compared with the buildup during pile irradiation. The alpha-particle energy (5.4 MeV) and the spontaneous fission half-life (< 1.2 x 10/sup 7/ years) of /sup 248/Cm are reported. The spontaneous fission half-life of /sup 254/Cf was found to be 55 days. No other mode of decay was observed for this isotope.

C. M. Stevens

Papers

The Isotopic Composition of Methane in Polar Ice Cores

Decay Properties of Plutonium-244, and Comments on its Existence in Nature

Solar neutrinos: proposal for a new test.

Nuclear constants of nine transplutonium nuclides

Transplutonium elements in thermonuclear test debris