E-Mail IMAGE: A transmitted light view through a 200-micron section of a peridotite sample, showing the three main minerals - olivine (clear-green), orthopyroxene (grey-green) and garnet (pink). view more Credit: Dr Emma Tomlinson, Trinity College Dublin. Geologists have developed a new theory about the state of Earth billions of years ago after examining the very old rocks formed in the Earth's mantle below the continents. Assistant Professor Emma Tomlinson from Trinity College Dublin and Queensland University of Technology's Professor Balz Kamber have just published their research in leading international journal, Nature Communications. The seven continents on Earth today are each built around a stable interior called a craton, and geologists believe that craton stabilisation some 2.5 - 3 billion years ago was critical to the emergence of land masses on Earth.