Earth history. Low mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals.

The oxygenation of Earth's surface fundamentally altered global biogeochemical cycles and ultimately paved the way for the rise of metazoans at the end of the Proterozoic. However, current estimates for atmospheric oxygen (O2) levels during the billion years leading up to this time vary widely. On the basis of chromium (Cr) isotope data from a suite of Proterozoic sediments from China, Australia, and North America, interpreted in the context of data from similar depositional environments from Phanerozoic time, we find evidence for inhibited oxidation of Cr at Earth's surface in the mid-Proterozoic (1.8 to 0.8 billion years ago). These data suggest that atmospheric O2 levels were at most 0.1% of present atmospheric levels. Direct evidence for such low O2 concentrations in the Proterozoic helps explain the late emergence and diversification of metazoans.

Widespread iron-rich conditions in the mid-Proterozoic ocean.

The chemical composition of the ocean changed markedly with the oxidation of the Earth's surface, and this process has profoundly influenced the evolutionary and ecological history of life. The early Earth was characterized by a reducing ocean-atmosphere system, whereas the Phanerozoic eon (less than 542 million years ago) is known for a stable and oxygenated biosphere conducive to the radiation of animals. The redox characteristics of surface environments during Earth's middle age (1.8-1 billion years ago) are less well known, but it is generally assumed that the mid-Proterozoic was home to a globally sulphidic (euxinic) deep ocean. Here we present iron data from a suite of mid-Proterozoic marine mudstones. Contrary to the popular model, our results indicate that ferruginous (anoxic and Fe(2+)-rich) conditions were both spatially and temporally extensive across diverse palaeogeographic settings in the mid-Proterozoic ocean, inviting new models for the temporal distribution of iron formations and the availability of bioessential trace elements during a critical window for eukaryotic evolution.

Is billboard advertising beneficial for healthcare organizations? An investigation of efficacy and acceptability to patients.

The healthcare industry is increasingly turning to billboard advertising to promote various medical services, yet little attention has been directed toward understanding the performance and policy implications of billboard advertising from the perspective of the patients targeted. To shed light on this, we initiated a field experiment investigating the impact of an urgent care center's billboard advertising campaign, collecting primary data over a 32-day period at the center's two clinics. Over the course of the billboard campaign, perspectives from 1,640 patients were collected via questionnaire. Institutionally supplied business metrics were also monitored. Our principal findings indicate that billboard advertisements are noticed by patients, favorably viewed by patients, and effective across the sequence of steps leading to patient patronage. Enhancement of awareness exerts the most powerful influence on patronage, but the capacity to inform consumers is also highly significant. These effects are not limited to new patients, as many returning clients were made more aware of the clinics and were influenced by the campaign. The study offers insights for creative billboard treatments and campaign planning. Although effects remained strong throughout the campaign, some degree of "wearout" was evident after three weeks, which suggests the need to rotate billboards frequently and to consider digital billboards. Corner tabs--small announcements sometimes placed in the corners of billboard advertisements--proved largely ineffective as a promotional device and may clutter the central messages. Given these findings, we believe healthcare institutions are justified in using billboards, as they perform effectively and appear relatively free of controversy. Careful planning of creative billboard treatments and appropriate scheduling patterns are essential to maximize their communications potential.