When introduced almost five decades ago, radiocarbon (14C) dating provided New World archaeologists with a common chronometric scale that transcended the countless site-specific and regional schemes that had been developed by four generations of field researchers employing a wide array of criteria for distinguishing relative chronological phases. A topic of long standing interest in New World studies where 14C values have played an especially critical role is the temporal framework for the initial peopling of the New World. Other important issues where 14C results have been of particular importance include the origins and development of New World agriculture and the determination of the relationship between the western and Mayan calendars. It has been suggested that the great success of 14C was an important factor in redirecting the focus of American archaeological scholarship in the 1960s from chronology building to theory building, led to a noticeable improvement in US archaeological field methods, and provided a major catalyst that moved American archaeologists increasingly to direct attention to analytical and statistical approaches in the manipulation and evaluation of archaeological data.

Half a century since radiocarbon was first used in the archaeology of the Old World, it seems that the expectations of W F Libby may be becoming a reality. In 1952 (Libby 1952:97), he wrote:

Archaeologists, geologists and palynologists are continually searching for the means to improve methods of counting time. The … relative chronologies lack precision and direct correlation with the calendar, except when they may be checked with, … for example, the calendar based on tree-ring counts.

For the majority of dating laboratories and their respective user communities, the journal Radiocarbon is no longer regarded as the medium for primary publication of radiocarbon measurements. In compliance with editorial policy, the emphasis has long since moved towards the publication of research papers on technological enhancements and applications of 14C as well as other cosmogenic isotopes and this has left a requirement for an alternative medium for the publication of date lists per se. In the late 1980s, an International Radiocarbon Data Base was proposed by Renee Kra (then the managing editor) but limitations in computer and communications technologies together with the inevitable financial implications meant that this timely concept could not be taken to completion. In the last year, we have taken advantage of the development of the worldwide web to compile a database of 14C age measurements of a Scottish archaeological nature which can be found at the web address http://www.historic-scotland.gov.uk/.

A new suite of five dates on a whale rib from Varangerfjord was completed on different fractions obtained by EDTA treatment. The intention was to test the possible influence of contaminants, the criteria for complete reactions, and the reliability of the treatment in light of scattered values obtained earlier on samples from Varangerfjord. The yield on the treatment of the selected bone did, however, not allow any general conclusions regarding the influence of contaminants in nature. The results are interesting from an inter-sample comparison point of view. Included are observations, made during treatment, of pH and color changes as well as the appearance of the samples. These observations are provided as a reference for deciding when the treatment is complete.

The publication during the 1990s of Greenland ice-core records spanning the transition from the Last Cold Stage to the present interglacial (ca. 14–9 14C ka BP) presented new challenges to scientists working on marine and terrestrial sequences from this important time interval. In particular, there is now an overriding imperative to increase the levels of precision by which events during this period can be dated and correlated. We review some of the problems commonly encountered when using radiocarbon dating for these purposes, and consider some of the new approaches that will be required if this dating method is to provide a basis for a high precision chronology for the last glacial-interglacial transition.

Climate on Earth strongly depends on the radiative balance of its atmosphere, and thus, on the abundance of the radiatively active greenhouse gases. Largely due to human activities since the Industrial Revolution, the atmospheric burden of many greenhouse gases has increased dramatically. Direct measurements during the last decades and analysis of ancient air trapped in ice from polar regions allow the quantification of the change in these trace gas concentrations in the atmosphere. From a presumably “undisturbed” preindustrial situation several hundred years ago until today, the CO2 mixing ratio increased by almost 30% (Figure 1a) (Neftel et al. 1985; Conway et al. 1994; Etheridge et al. 1996). In the last decades this increase has been nearly exponential, leading to a global mean CO2 mixing ratio of almost 370 ppm at the turn of the millennium (Keeling and Whorf 1999).

This paper provides a summary overview of the current state-of-art in the radiocarbon dating of groundwater. While the use of natural 14C measurements in applied hydrogeology still presents a difficult challenge, meaningful dates can be achieved if they are determined and interpreted in conjunction with the analyses of other isotopic species that occur in the natural environment. Although 14C dating of groundwater can be, and often is, carried out as a matter of routine, any specific case study requires its own scientific design and effort. As is widely recognized, and discussed in considerable detail throughout the scientific literature, there are many hydrogeochemical reactions and/or physical processes that can alter the natural 14C enrichment measured in environmental materials. Fortunately, for fresh groundwater resources such effects are in general well defined and therefore of limited significance. The primary challenge in applied groundwater dating is with the development of the appropriate theoretical background against which 14C dates can be used to calibrate numerical analogues of the groundwater system. The hydraulic properties of each of the widely used finite-element models can be well estimated from numerous piezometric data and extrapolations. In contrast, only a few groundwater ages can be provided for the calibration of those models that are complex functions of aging mixture and sometimes also hydrochemical reactions.

A review is given of some critical events in the development of radiocarbon aerosol science, and the profound influence of radiocarbon accelerator mass spectrometry (AMS) on its current applications and future prospects. The birth of this discipline occurred shortly after the initial development of 14C dating. Unlike dating, which is founded on the continual decay of 14C and the resulting full range of 14C/12C ratios in once-living matter, 14C applications to atmospheric aerosol research relate primarily to the determination of mixing ratios of fossil and biomass components. Such determinations have come to have major importance in work ranging from the resolution of woodburning and motor vehicle components of urban particulate pollution, to the apportionment of radiation-forcing (black) particulate carbon from natural wildfires and anthropogenic regional plumes. The development of this area has paralleled that of AMS itself, with the one or the other alternately serving as the driving force, in a sort of counterpoint. The remarkable million-fold improvement in sensitivity made possible by AMS has become critical in meeting rapidly emerging societal concerns with the origins and effects of individual carbonaceous species on health and climate.

This paper discusses some aspects of the development of accelerator mass spectrometry (AMS), the international conferences that have been held, and the books that have been written on the subject. It also mentions some details of the technique and its strengths. Some of the interesting measurements that have been made recently are covered, and finally, it presents some thoughts on future developments.

This paper includes a brief history of the calibration of the radiocarbon time scale from the first recognition of the necessity of calibration in 1962 to INTCAL98. Thirty-six years of effort by dendrochronologists and the 14C community have pushed the tree-ring calibration back to 11,854 yr BP. All of this part of the calibration has been done by high-precision beta counting. Uranium-thorium (U-Th) dating of coral samples coupled with accelerator mass spectrometry (AMS) measurement of 14C has extended a fairly detailed calibration back beyond the Bølling warm episode to 15,000 BP. Earlier than 15,000 BP, piecewise linear approximation extends INTCAL98 calibration to 24,200 BP.

Blending 1-, 2-, 3-, 10-, and 20-yr tree-ring samples containing regional and data offsets into a decadal time scale does not make an ideal error and bias free δ14C record. Nevertheless, spectral analysis reveals some statistically significant fundamental frequencies as well as interesting “beat” frequencies and the second harmonic of the around 208-yr cycle that is considered to be solar in origin. Although, some very prominent peaks such as the 88-yr (Gleissberg) are clearly solar in origin, some of the lower frequencies such as of the 512-yr period may have an origin in thermohaline circulation. Thus, INTCAL98 provides useful data for geophysical and solar physics research. Lastly, single year δ14C analysis would be useful for revealing invaluable information for solar physics, astrophysics and geophysics not accessible by decadal data. We provide several examples.

In this paper, we review the production of radiocarbon and other radionuclides in extraterrestrial materials. This radioactivity can be produced by the effects of solar and galactic cosmic rays on solid material in space. In addition, direct implantation at the lunar surface of 14C and other radionuclides can occur. The level of 14C and other radionuclides in a meteorite can be used to determine its residence time on the Earth's surface, or “terrestrial age”. 14C provides the best tool for estimating terrestrial ages of meteorites collected in desert environments. Age control allows us to understand the time constraints on processes by which meteorites are weathered, as well as mean storage times. Third, we discuss the use of the difference in 14C/12C ratio of organic material and carbonates produced on other planetary objects and terrestrial material. These differences can be used to assess the importance of distinguishing primary material formed on the parent body from secondary alteration of meteoritic material after it lands on the earth.

In this short article, we summarize some milestones in the 50-yr-long development of natural 14C measurement. In the light of this appraisal we presume to hazard some personal opinions and forecasts as to where best opportunities might lie for future gains from the continued investment in applied 14C science. The technique and the journal are one and the same in this regard.

New Laboratory

A new laboratory has opened in Miami, Florida. Ronald Hatfield and Darden Hood are the Directors of BIOCAMS International, which provides “AMS dating designed exclusively for art, antiques, and materials of potential commercial value”. See http:/www.biocams.com/ for details.