Scientists studying ancient rocks from Western Australia have found signs that water was reaching deep inside Earth more than three billion years ago. The rocks preserve chemical evidence that water-rich crustal material periodically sank into the mantle, where it could fuel volcanic activity. This process appears to have been underway long before modern-style plate tectonics may have fully developed.
The researchers propose that pieces of water-laden crust were pulled downward into the mantle through a mechanism that operated on the early Earth. This would have allowed water to influence melting and volcanic output at a time when the planet's interior dynamics were likely very different from today.
The findings push back the timeline for deep water cycling and raise new questions about how Earth's early volcanic systems were powered. They also suggest that the connection between surface water and mantle processes may be far older than previously assumed.