The vast oceans, seemingly endless and unfathomable, cover nearly three-quarters of the Earth's surface and contain 96.53% of the planet's total water. So, where does all this water come from? Early beliefs held that this water was inherent to Earth, forming as the planet coalesced from the primordial solar nebula. However, modern research indicates that this water does not originate directly from within the Earth but rather from the recycling of surface water. Geological studies of celestial bodies show that Earth's neighbors, such as Venus, Mercury, and Mars, are all water-poor, while Earth is uniquely endowed with abundant water.
Scientists have differing opinions on this matter. One view suggests that the water on Earth was brought by comets. Recent studies indicate that approximately 1,000 cubic meters of cometary material enters Earth each year, which seems to far exceed the current total volume of ocean water. However, this claim still requires further validation.
Another perspective posits that the water on Earth is inherent. Although volcanic steam and hot spring water primarily result from surface water cycling, there may also be a small amount of 'primordial water.' If Earth has maintained its current volcanic activity, the accumulated water over billions of years could reach 100 times the current total volume, suggesting that 1% of this 'primordial water' might constitute a major source of ocean water.
Additionally, there is a hypothesis that Earth's water has undergone multiple cycles of drying and resurgence. Chinese scholar Dong Miaosheng proposed the 'Multi-Season Theory,' which suggests that Earth has periodically transferred its biosphere and water resources to other planets and then returned. This hypothesis attempts to explain the source of water on Earth but still requires more evidence to support it.
