Scientists built a model of Earth with all living organisms removed — from bacteria to trees. Over billions of years, this 'empty house' didn't turn into an icy desert. Volcanoes, like a furnace, release carbon dioxide, and rock weathering, like a thermostat, absorbs it. These processes maintain a comfortable temperature and liquid water without any help from the biosphere.
The real trick is in the light. The planet reflects sunlight, and this rainbow fingerprint looks like life is bubbling away. Even the most sensitive future telescope, Habitable Worlds Observatory, could be fooled, mistaking a geological illusion for a biosignature. So the search for extraterrestrial intelligence might stumble upon an empty but cozy world that simply pretends to be alive.
Even if all life vanished, Earth would still send a light 'hello' into space for billions of years — one that astronomers would mistake for a sign of a biosphere.