Abstract

Earth-sized planets are common in the Universe. However, we do not yet know in detail what they are made of, or why. This may be crucial for assessing their habitability. A case in point is the low carbon abundance of Earth: while it is essential to life, too much carbon may adversely affect habitability. Most planetary abundance anomalies likely originate in the protoplanetary disk stage, but the processes involved are not yet well constrained by observations. I will present recent results on elemental abundances in disks, focussing on the carbon and oxygen abundances and a novel look at the composition of gas and dust in the inner 1 astronomical unit. I will conclude with a discussion of the implications for our understanding of planetary systems, and a preview of upcoming developments.