One hypothesis claims that Earth accreted (gradually grew by accumulation of) icy planetesimals about 4.5 billion years ago, when it was 60 to 90% of its current size. In this scenario, Earth was able to retain water in some form throughout accretion and major impact events.
The theory proposes that Earth grew by accumulating icy planetesimals over time, retaining water throughout the accretion process and major impact events.