What We will study the composition of rocky planets similar to Earth. Life originated on our planet more than 4 billion years ago. We want to understand what the conditions are on the surface of such young planets. We will therefore make computer calculations that explain the composition of the core, mantle and atmosphere of potentially habitable planets. Rocky planets gather both water and organic molecules as they grow. These molecules are initially dissolved in a deep magma ocean that extends from the surface of the planet down to the core. We will model how these molecules are outgassed from the magma ocean to form the first atmosphere when the magma cools and crystallises. Why Astronomers know today of more than 5,000 "exoplanets" -- planets that orbit stars other than the Sun. The hunt is on to find the first planet akin to Earth that may host life outside of the Solar System. The next generation of telescopes, including the James Webb Space Telescope that was launched in 2021, will be able to measure, for the first time, the composition of atmospheres around small exoplanets similar to Earth. Members of our team have played key roles in formulating a new planet formation theory where rocky planets grow by collecting millimetre-sized pebbles, and on shedding light on the composition of planets and their building blocks. We are therefore in a unique position to combine our expertises in an interdisciplinary project to make major progress in understanding the composition of rocky planets and their atmospheres. How We will calculate how rocky planets grow by collecting pebbles of millimeter sizes. They also grow in giant impacts between smaller proto-planets. The pebbles are cold and have rims of ice, similar to hail stones. They also carry in them simple organic molecules rich in carbon and nitrogen. We will model how rock, metal, ice and organic molecules evaporate during the formation of the planet and what fraction of these components actually survive to become part of the planet. We will then first calculate how much water, carbon and nitrogen is dissolved in the core of the growing planet and how much is dissolved in the magma ocean. Finally, when the magma ocean crystallises, we are able to calculate the composition of the molecules that are outgassed from the magma ocean. These will mainly be H2O, H2, CO2, CO and N2. We will calculate the pressure of the atmosphere and its composition for planet masses ranging from lighter than Earth to heavier than Earth. Many rocky exoplanets are known to orbit stars that are colder than our Sun, the so-called M-dwarf stars. We will therefore calculate the composition of planets hosted both by Sun-like stars and by M-dwarf stars.