Images Dated 25th January 2006

IUD contraceptive and sperm cells

IUD contraceptive and sperm cells. Computer artwork of an intrauterine device (IUD, red and white, centre) in a woman's uterus, surrounded by sperm cells (white, not to scale). The IUD is a contraceptive device that is implanted in the uterus to prevent pregnancy. It does not interfere with the sperm cells (male reproductive cells), one of which may fertilise an egg cell (female reproductive cell). However, when a fertilised egg tries to implant in the wall of the uterus, the shape and material of the IUD disrupts this process. This IUD has a coil (red), made of a metal such as copper. If the implantation fails, the fertilised egg is lost during menstruation. This view looks upwards into the uterus. The loop and string at bottom are used to remove the IUD if it is no longer needed

© CHRISTIAN DARKIN/SCIENCE PHOTO LIBRARY

Surface of Callisto, a Jovian moon

Surface of Callisto. Computer artwork of craters on the surface of Callisto, one of the moons of Jupiter. Callisto has a heavily cratered surface, formed as rocky debris impacts it from space. The large mass of Jupiter is thought to attract comets and asteroids, some of which impact on its moons. The preservation of these craters implies that Callisto has little or no geological activity

© CHRISTIAN DARKIN/SCIENCE PHOTO LIBRARY

Earth after global warming

Earth after global warming. Computer artwork of a future Earth where the ice-caps have melted due to global warming. Greenland (green, upper left) has lost its ice-cap, and the Arctic Ocean is free of sea ice. Although global warming can be part of a natural cycle, many scientists believe that human activities have contributed to the observed global warming. Industrial pollution has increased levels of the greenhouse gas carbon dioxide. This traps the Sun's heat in the atmosphere, preventing it from being radiated back out from the ground into space. A rise in the average temperatures by a few degrees Celsius could melt the ice caps in a few hundred years, causing large rises in sea levels, plus more storms (hurricane, lower left) and increased desertification (Sahara, lower right)

© CHRISTIAN DARKIN/SCIENCE PHOTO LIBRARY