Rainer Berger

Replacement Rates for Human Tissue from Atmospheric Radiocarbon

Carbon-14, derived from the testing of thermonuclear weapons in the atmosphere of the Northern Hemisphere during 1961-62, has been found in human tissues including the brain in amounts which reflect the atmospheric concentration of carbon-14 as of several months earlier. In collagen of cartilage, the rate of uptake of carbon-14 is much slower than in other tissues; essentially no radioactive carbon was found in the collagen of 70-year-old adults that had been exposed to the comparatively high concentrations of carbon-14 in the atmosphere during the years 1954 to 1964. Individuals from the Southern Hemisphere show little increase in the carbon-14 content of their tissues at present, and detailed tests with individuals traveling to the Northern Hemisphere from the Southern allow closer scrutiny of the tissue replacement rates.

Late pleistocene history of coniferous woodland in the mohave desert.

Seventeen ancient wood-rat middens, ranging in radiocarbon age from 7400 to 19,500 years and to older than 40,000 years, have been uncovered in the northeastern, north-central, southeastern, and southwestern sectors of the Mohave Desert. Excellent preservation of macroscopic plant materials (including stems, buds, leaves, fruits, and seeds) enables identification of many plant species growing within the limited foraging range of the sedentary wood rat. An approximately synchronous zonal differentiation of vegetation in response to a gradient of elevation on limestone in the northeastern Mohave Desert is apparent from the macrofossil evidence, preserved in wood-rat middens and ground-sloth coprolites, covering a time span bracketed by radiocarbon ages of about 9000 and 10,000 years. XerophilQus juniper woodlands descended to an elevation of 1100 meters, some 600 meters below the present lower limit of woodland (1700 meters) in the latitude of Frenchman Flat. But desert or semidesert shrubs coexisted with the woodland trees throughout much of the span of elevation corresponding to the pluvial lowering of the woodland zone, and the more mesophytic phase of pinyonjuniper woodland was evidently confined to montane habitats at elevations above 1500 meters. Joshua trees, accompanied by desert shrubs, prevailed down to about 600 meters at Gypsum Cave, Nevada, but only the shrubs of the existing warm-desert vegetation occurred at 530 meters near Rampart Cave, Arizona. Pleistocene middens from the southeastern Mohave Desert record a relatively large downward shift of the pinyon-juniper woodland zone, paralleling the remarkably low minimum elevation of the existing woodland zone in that area. The macrofossil evidence speaks for former continuity of the many disjunct stands of woodland vegetation in the Mohave Desert region, at least along the higher divides connecting most of the ranges. However, there is no macrofossil evidence of pluvial continuity of range for the more mesophytic, montane, coniferous-forest zone of ponderosa pine or white fir now occupying islands of relatively mesic environment on the highest mountains of the region. On the contrary, the uneven stocking of the lofty mountains of the Mohave Desert with mesephytic or boreal species and the trend toward endemism suggest a long history of isolation.

Radiocarbon Content of Marine Shells from the California and Mexican West Coast

The radiocarbon content of contemporary pre-bomb marine shells from the upwelling environment of the California and the West Mexican coast has been determined. In addition, factors leading to the apparent ages of different magnitude for various marine environments are discussed.

UCLA Radiocarbon Dates V

Radiocarbon measurements carried out during 1965 are reported on archeologic-historic samples from California, Nevada, Mexico, Peru, Brazil, Philippines, Spain, England, Egypt, and Africa. Geophysical, geological-climatological and biological measurements are given for: C-14 in atmospheric carbon dioxide (California), bomb C-14 in foodstuffs (California, Australia, Colombia), bomb C-14 in human tissues (widespread localities), bomb C-14 in plants (Colorado), oceanic measurements (California, Mexico), vegetation and climate (California, Texas, Nevada), and geological processes (California, Israel).

Radiocarbon Dating of Bone and Shell from Their Organic Components

A method of dating bone and shell by radiocarbon content has been developed. The mineral is removed by mild acid treatment and the residual carbon is dated in the usual manner.

Geomagnetic Intensity: Changes during the Past 3000 Years in the Western Hemisphere

A series of archeomagnetic measurements have been carried out on archeologic materials from Arizona and Mexico which can be compared with results from Europe and Asia. This comparison shows a westward drift of geomagnetic intensity at a rate of about 0.24 degree per year. Furthermore, an apparent coincidence between changes in the earths magnetic moment and changes in the production rate of radiocarbon is observed.

RADIOCARBON CONTENT OF MARINE SHELLS FROM THE PACIFIC COASTS OF CENTRAL AND SOUTH AMERICA.

The radiocarbon content of contemporary pre-bomb marine shells from the region of upwelling of the Pacific coast of South America has been determined and found to be somewhat similar to the content of shells from the coast of California and the west coast of Mexico. Deviations of up to -8.5 percent with reference to the contemporary biospheric carbon-14 standard have been observed for the Peruvian coast. Values of from -0.35 to -4.04 percent have been obtained for marine shells from the Gal�pagos group. Problems associated with radiocarbon dates based on shells are discussed.

Equilibration of Atmospheric Carbon Dioxide with Sea Water: Possible Enzymatic Control of the Rate

Surface and subsurface ocean water differ in exchange characteristics with atmospheric carbon dioxide. The possibility of control by an enzyme like carbonic anhydrase has been experimentally explored.

UCLA radiocarbon dates IV.

Reports of carbon-14 dating are grouped under archeologic-historical dates and under geophysical, geologic, and biologic measurements. Samples studied in the first group came from the United States, Mexico, South America, the Pacific, Europe, Asia, and Africa. The second group included studies of carbon-14 in the atmosphere in California and Galapagos Islands, bomb radiocarbon in human tissues; plants and seaweed from California; seawater off Baja California, Mexico; tree rings from Arizona and California; vegetation and climate, southwestern United States; geologic processes as shown in samples from California and Wisconsin.

Radiocarbon Dating of Petroleum-Impregnated Bone from Tar Pits at Rancho La Brea, California

A liquid-chromatography method has been developed for the separation of amino acids with the same specific activity in radiocarbon from bones impregnated with isotopically dead petroleum compounds found in the La Brea tar pits. This technique permits the application of radiocarbon dating to such bone assemblages.