Question

All intelligent life is multi-cellular, and multi-cellular life is only possible if the cells have the capability of producing energy. The cells in present day humans, animals, and plants, examples of complex cellular life, require oxygen to break nutrients down and create energy. Since the earths environment consisted almost entirely of carbon dioxide prior to the wiwaxia event, there is little chance that any intelligent life existed on earth prior to the wiwaxia event.

Answer 1

There might be any intelligent species around us but can be microscopic otherwise we would have seen it earlier.