Complex sentence: The extraterrestrials transform the earth in favor of its living conditions, burning forests, destroying cities, and building megastructures that slowly terraform the Earth, pumping out methane, making it harder and harder to breathe, while flooding cities near the oceans.
Split into simpler sentences: The extraterrestrials transform the earth in favor of its living conditions. They burn down forests, destroy cities and build huge megastructures that are slowly terraforming the Earth, pumping out methane and making it harder and harder to breathe and flooding cities close to the oceans.