Terrestrial planets

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  • An extrasolar planet or exoplanet is a planet orbiting a star (or remnant of a star) beyond our Solar System. As of autumn 2007, about 250 exoplanets had been discovered around 220 different stars, including nearly two dozen multiple planet systems. No less than five exoplanets have been discovered orbiting the star 55 Cancri; one of the planets has nearly four times the mass of Jupiter, another is comparable with Jupiter in mass, two are slightly less massive than Saturn, while the innermost planet has a mass similar to that of Uranus....

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  • The same amount of water has been present on our planet for about 4 billion years, since shortly after the Earth was formed. Since then it has cycled through evaporation, condensation, precipitation and surface runoff multiple times. Water scarcity as an abiotic factor ranging from moderate to severe stress levels, accompanied by loss of moisture in the soil, is extremely hard for most organisms to cope with, particularly terrestrial plants and their food-chain dependents.

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  • Water contamination weakens or destroys natural ecosystems that support human health, food production, and biodiversity. Studies have estimated that the value of ecosystem services is double the gross national product of the global economy, and the role of freshwater ecosystems in purifying water and assimilating wastes has been valued at US$ 400 billion (2008$) (Costanza et al. 1997). Freshwater ecosystems are among the most degraded on the planet, and have suffered proportionately greater species and habitat losses than terrestrial or marine ecosystems (Revenga et al. 2000).

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  • Flowering plants now dominate the terrestrial ecosystems of the planet, and there are good reasons for supposing that the flower itself has been a major contributing factor to the spread of the Angiosperms. Although the Angiosperm flower is based on four whorls of organs – petals, sepal, stamens and carpels – the 300 000 odd species exhibit a huge array of different floral morphologies. Consider, e.g., the humble periwinkle flower and contrast it with the complex passion flower.

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