№ 220/2013 from Jul 30, 2013
Carbon, hydrogen, and nitrogen are the building materials for life on our planet. Until recently, the time of arrival of these elements on the Earth and their source, asteroids or comets, was uncertain. But new research shows that a significant fraction of these elements arrived relatively late on Earth, after the formation of its core.
By determining the ratios of closely related elements in the Earth’s mantle, geochemists Zaicong Wang and Harry Becker of Freie Universität Berlin have concluded that the elements so essential to the construction of life were delivered by material with compositions similar to some carbon- and water-rich meteorites. The new research, published in the journal Nature, suggests that at least 20% to possibly 100% of the total amounts of carbon and hydrogen arrived late on the Earth, as the result of collisions with asteroids between 4.5 and 3.8 billion years ago.
Nature, July 18, 2013, vol. 499, 328-331.