ImageWriting in Nature's News and Views, Assistant Professor Dr. Katherine Bermingham—an authority on cosmo- and geo-chemistry—comments on how the isotopic composition of very ancient rocks from Greenland help understand the building blocks of Earth. Particularly interesting is the origin of volatile compounds like water and organics, which could have arrived by carbonaceous chondrite (meteorite) collisions during the final stages of our planet's growth billions of years ago. click here for paper