The early evolution of the Earth resulted in a planet where life could arise and evolve. The evolution of life led to feedbacks between organisms and their environment, which shaped the chemical nature of Earth and contemporary life. Many steps in the coevolution of life and planet are still poorly understood. Here, we focus on three aspects. Impacts have shaped the early Earth, delivered water and carbon, but also affected biodiversity later in Earth’s history. We combine past impact events with orbital parameters and physical compositions of near- Earth objects to assess how future impacts may affect biodiversity. The emergence of multicellularity has spurred a large increase in biodiversity. How unicellularity evolved towards multicellularity is still largely unknown. 2.5 to 2.1 billion years ago small amounts of oxygen were pumped into the atmosphere by cyanobacteria. We experimentally investigate how these low, variable oxygen levels may have promoted the evolution of multicellularity. The evolution of multicellularity, itself depending on symbioses, spurred an unprecedented potential for interactions among organisms, especially between multicellular hosts and microbial symbionts: host-microbiome interactions. We elaborate on how evolution of multicellular hosts changes the composition of unicellular symbiont communities and, thus, shapes the complexity of current day life.
