# Tweet by [@keefmoon](http://twitter.com/keefmoon) on 2021-09-04 11:15:49 > [!INFO] Archived from [original tweet](http://twitter.com/keefmoon/status/1434112964655828998) I've always thought the Eukareotic event, when simple cells become complex cells, is likely a "great filter". A possible reason why complex life in our galaxy might be very rare. Could the Great Oxidation could be another filter? Anyone have a better understanding than me?