Calcium is one of the most abundant elements on Earth. It plays various roles in many organisms, whether for the contraction of muscle cells, preserving potential differences across membranes, as a co-factor for some enzymes, or a component of bones and shells, to name a few.
Yet, it is surprisingly scarce in the upper atmosphere. Why could that be? Don’t anxiously skip to the end of this post for the answer… this scarcity remains unexplained for now. In this month’s ‘in your element’ article (subscription required) John Plane, Professor of Atmospheric Chemistry at the University of Leeds, ponders on this mystery.
All of the calcium that is present in the upper atmosphere has actually been brought there by interplanetary dust particles entering the Earth’s atmosphere, in a process called ‘meteoric ablation’. The intriguing data is that the concentration of calcium is much lower than expected — about 200 times lower than that of sodium for example, whereas they are present in roughly the same concentrations in the Earth’s crust. Check out the article to find out how scientists measure metal concentrations in the atmosphere.
Could the interplanetary dust particles be depleted in calcium before they even come in contact with our atmosphere? Could it be that more volatile elements (such as sodium) get ablated from the meteorites much more easily than calcium? Or an effect of a peculiar atmospheric reactivity for calcium? Plane explains how some of these reasons are valid, but only to some extent — and so the depletion in calcium has not yet been entirely accounted for.
Anne Pichon (Associate Editor, Nature Chemistry)