There would be little to no oxygen. All life would be deep enough in the oceans that they were safe from the destructive effects on DNA that UV light causes. Before there was enough oxygen in the atmosphere all life was in the ocean. Near the surface of the water was a toxic zone during daylight hours. Before photosynthesis the food chain started by the ionization of dissolved chemicals in hydrothermal vents totally independent of the toxic sunlight. At some point life deep enough to beside from UV light started photosynthesizing longer wavelengths of light for their energy source. This gradually added oxygen to the atmosphere. As oxygen accumulated life could live closer and closer to the surface. Eventually we had enough oxygen in the atmosphere for an ozone layer allowing terrestrial life to exist. So if no evolution to do photosynthesis evolved, the Earth’s atmosphere would have little oxygen, and likely still have 10 times as much CO2 as it does now.