What would happen if no carbon dioxide was the air?

If there were no carbon dioxide (CO2) in the air, photosynthesis would cease, as plants rely on CO2 to produce oxygen and food. This would lead to a collapse of ecosystems dependent on plant life, severely diminishing the food supply for herbivores and, subsequently, carnivores. Additionally, the Earth's temperature would drop significantly, as CO2 plays a crucial role in trapping heat in the atmosphere. Overall, the absence of CO2 would disrupt the balance of life on Earth and could lead to a mass extinction event.