In the Matty's Paradigm narrative cellular life originates in water in zero-G, before there was an atmosphere. Here's some science lingo attempting to explain super-sized prokaryotic cells in an environment with no oxygen.
Life Before Oxygen
Life before oxygen: Fossils of 2.5 billion-year-old bacteria reveal organisms thrived despite early Earth’s harsh conditions
Geologists found large spherical fossils thought to be from microbial life. Microbes lived in the ocean depths before Earth's oxygen-rich atmosphere. Researchers claim they are the oldest bacteria of their kind to be found.