A magnetic bubble
Moving liquid iron in the outer core generates Earth's magnetic field. That field reaches far into space and forms the magnetosphere — a shield around the planet.
Two ways it protects Earth
1. It deflects the solar wind (a stream of charged particles from the Sun). 2. It blocks harmful radiation / cosmic rays from space. A third true bonus: it helps keep the solar wind from stripping away the atmosphere. Write two of these on the test.