Here’s how you could frame an argument using mainstream science concepts to prove aliens created many lifeforms

Using mainstream science, we can argue that the universe, after its creation, experienced a timeline where nothing existed for billions of years. During this vast period, life eventually formed on a planet, a phenomenon observed through natural processes such as chemical evolution and abiogenesis. Though many life forms went extinct, one advanced civilization survived. Over potentially 30 billion years, this civilization mastered time travel. They then traveled back in time to seed life on other planets. This hypothesis aligns with known scientific principles and does not contradict our current understanding of physics and biology, allowing for the possibility of such events occurring.