PNAS

Front Matter

News Feature: Life after the asteroid apocalypse

Sixty-six million years ago, an asteroid wiped out a huge swath of life on planet Earth. But could this and similar impacts have helped kick-start life itself?

Image courtesy of Detlev van Ravenswaay/ScienceSource.

Core Concept: “Twisted” light beams promise an optical revolution

Twisted light is being used to build optical tweezers and ultra-powerful microscopes, and it could eventually be used in microscale machinery and for novel spectroscopic analyses. But optical communications is likely to be its most important application.

Image courtesy of Mario Krenn (University of Vienna, Vienna).

Inner Workings: Microscopy lights up stem cells in action

In the midst of a microscopy boom, stem cell researchers are coming up with inventive techniques for capturing live images of these enigmatic cells in their native habitats.

Image courtesy of Panteleimon Rompolas (University of Pennsylvania, Philadelphia).

In the News

Archaeological finds illuminate Roman Empire battle

Archaeological excavations in Denmark shed fresh light on a fierce battle in Northern Europe in the first century AD. Cut marks on bones and hip bones threaded on a stick hint at the possibility of ritual in the disposal of human remains, according to the authors.

Lead pollution in Greenland ice tracks historical events

Researchers report links between records of lead pollution in Greenland ice cores and economic fluctuation in ancient societies. The record of European lead pollution in Greenland ice provides insights into ancient economic activities, including lead and silver mining.

Global biomass distribution

Researchers report a census of biomass on Earth, and comparison of the census with historical biomass estimates suggests that human activities have led to reductions in wild mammal, fish, and plant biomass, according to the authors.

Image courtesy of Pixabay/bildgebende_Momente.