Where Did Earth’s Water Come From?

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Where did the earth get all those volatile substances--nitrogen, hydrogen, water, carbon--necessary for the development of life and living things? The question has vexed scientists for a long time. Current theories invoke external sources, ice and other debris in the form of asteroids and comets bringing these materials to a young earth.  But a new theory is making the rounds (via Chemistry World):

Now, a new study led by Conel Alexander at the Carnegie Institution of Washington, US, has taken a significant step towards solving the conundrum.  Alexander’s team compared the hydrogen isotope ratios in chondritic meteorites, ancient fragments of asteroids, with those that have been measured in comets. In the outer Solar System, the birthplace of comets, the extreme cold results in frozen water having a higher proportion of deuterium than ice formed in the less cold regions. ‘We can measure the hydrogen isotope ratio of ice in comets remotely by infrared and submillimetre spectroscopy. We can measure the ratios in meteorites by analysing the hydrogen that is there – which is typically in the form of hydrated silicates, such as clays, that are the remnants of ancient water,’ explains Alexander. The team analysed the hydrogen isotope ratios in 86 meteorites, and showed that the proportion of deuterium to hydrogen was lower than in comets. ‘So, if we seem to have ruled out comets as a source of Earth’s volatiles, that leaves asteroids. We also analysed the nitrogen isotope ratios of the meteorites. We found that of the various types of chondrite the hydrogen and nitrogen isotopic compositions of one type, the CI chondrites, tallied most closely with what we see on Earth, suggesting that the parent bodies – asteroids – of these types of meteorite were the dominant source of the Earth’s volatiles.’

Other experts are intrigued and impressed by the work. Philip Bland of Curtin University in Australia says: ‘This is a really nice piece of work, a fascinating contribution to an old question – where did Earth’s water and organic material come from? The work is especially timely as it places compositional constraints on recent dynamical models of early Solar System evolution, contradicting a number of their predications.’


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One Response to Where Did Earth’s Water Come From?

  1. Dave says:

    How much of the Earth’s water is due to the Earth intercepting the solar wind (Hydrogen particles), and reacting them with Oxygen to produce water?

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