Complex sentence: Biologically, plants and other photoautotrophs extract the carbon from the atmosphere and use it for the construction of their body parts through the process of photosynthesis so Earth likely wouldn't have a present-day biosphere without atmospheric carbon dioxide.
Split into simpler sentences: Biologically, plants and other photoautotrophs extract the carbon from the atmosphere and use it for the construction of their body parts through the process of photosynthesis. Therefore, Earth wouldn't have a present-day biosphere without atmospheric carbon dioxide.