Abstract

e live on a wonderful planet that not only teems with life but shows a marvellous exuberance of form and variety. In comparison with the size of the Earth its living skin (the so-called biosphere) may be thin, but it is by no means negligible. From high in the atmosphere, where ballooning spiders wafted aloft on their silk-strings have been trapped at heights of more than 4500 m and birds such as condors cross tropical storms at altitudes well above 6000 in, via the oceans and the green continents, to deep within the Earth's crust where bacteria are known to live at depths of at least several kilometres, life is pervasive.