Here’s the theory

Guinan and her research team think it’s possible that asteroids that impacted Earth over the last few billions of years may have periodically forced Earth material — holding things like plant cells and single-celled organisms — into space, and that if a tiny amount of those cells survived the harsh journey through space, they could’ve reached Venus. If true, those robust cells may still be living in Venus’ atmosphere. Some could have even conglomerated together, speckling the world with the organics we have long assumed are confined to ours.