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2 results

  • 12 - How Many Inhabited Planets?

  • from Part III - Planetary Systems and Life
  • Wallace Arthur, National University of Ireland, Galway
  • Book:
    The Biological Universe
    Published online:
    24 September 2020
    Print publication:
    24 September 2020, pp 186-202

  • Summary

    Here, I ask the question: how many planets are there with life in the Milky Way? This question has many variants. We can ask about simple microbial life. Alternatively, we may ask about more complex life – for example multicellular animals and plants. Then again, we may ask specifically about intelligent life. An approach that can be used for all of these variants is the one pioneered by the American astronomer Frank Drake. In this chapter, I use the Drake equation to estimate the number of microbial worlds and the number of worlds with animals. (In a later chapter I use the same approach to estimate the number of worlds with intelligent life.) When Drake first devised his equation, we were hard put to come up with meaningful numerical values for any of its parameters. Now we have reasonably good values for at least some of them. Hence our estimates are better than before. However, there are still wide errors, so I investigate the effects of these errors on our estimates. Bearing them in mind, I only attempt estimates to the nearest order of magnitude. These estimates are: 1 billion planets with microbial life; and 10 million planets with animal life.

  • 1 - The Scandinavian Landscape and its Resources

  • from PART I - THE GEOGRAPHY AND PREHISTORY OF SCANDINAVIA
  • Edited by Knut Helle, Universitetet i Bergen, Norway
  • Book:
    The Cambridge History of Scandinavia
    Published online:
    28 March 2008
    Print publication:
    04 September 2003, pp 13-42

  • Summary

    Human intelligence exercises a decisive influence on the ecological balance of the landscape, to store knowledge and to organise the use of natural resources. This chapter starts by considering some of the main physical characteristics of the Scandinavian landscape throughout the millennia that have passed since the Quaternary glaciations. A number of physical processes were responsible not only for the geological construction of the Scandinavian landscape but also for the later changes that took place. The soils in Scandinavia consist mainly of relatively coarse glacial deposits, which have generally proved difficult to cultivate. In the last 5,000 years, shore displacement around the Baltic has mainly been caused by land uplift. However, the Norwegian Sea has not undergone such drastic changes. The chapter also deals with the climatic changes, coastal landscapes, and the vegetation zones and animal life in the Scandinavian region.