Waters and Stafford (Reports, 23 February 2007, p. 1122) provided useful information about the age of some Clovis sites but have not definitively established the temporal span of this cultural complex in the Americas. Only a continuing program of radiometric dating and careful stratigraphic correlations can address the lingering ambiguity about the emergence and spread of Clovis culture.

The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods). Some of these rocks are sedimentary, and include minerals which are themselves as old as 4.1 to 4.2 billion years. Rocks of this age are relatively rare, however rocks that are at least 3.5 billion years in age have been found on North America, Greenla...

Human modification of natural landscapes has influenced surface processes in many settings on Earth. Quantitative data comparing the distribution and behavior of geologic phenomena before and after human arrival are sparse but urgently required to evaluate possible anthropogenic influences on geologic hazards. We conduct field and imagery-based mapping, statistical analysis, and numerical model...

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Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements-has been in widespread use for over half a century. There are over forty such techniques, each using a different radioactive element or a different way of measuring them. It has become increasingly clear that these radiometric dating techniques agree with each other and as a whole, prese...

The development of flexible electronics operating at radio-frequencies (RF) requires materials that combine excellent electronic performance and the ability to withstand high levels of strain. In this work, we fabricate graphene field-effect transistors (GFETs) on flexible substrates from graphene grown by chemical vapor deposition (CVD). Our devices demonstrate unity-current-gain frequencies, ...

Among radio amateurs digital meteor burst communication has been discussed for many years. Despite this, no experiments on amateur basis have (to the knowledge of the author) been performed in Sweden or elsewhere in the world. During the past two years several amateurs have reported the random appearance of AX.25 packets from very distant stations. The propagation of these packets can only be e...

How to tell time: • Relative Time: putting events in time order. • Law of Superposition • Correlation of rock layers using fossils. William Smith " There is a wonderful order and regularity with which nature has disposed of fossils and assigned to each its peculiar stratum. " How to tell time: • Absolute Time: Determining age in years.