Geologists have discovered evidence that surface water was being recycled into Earth’s interior more than 3.1 billion years ago, driving volcanic activity long before the establishment of modern plate tectonics. The findings, published in Nature Communications, were based on the analysis of ancient volcanic rocks from the Pilbara Craton in Western Australia.
An international research team led by Dr. Eric Vandenburg, a geochemist at Adelaide University’s School of Physics, Chemistry and Earth Sciences, examined the Whundo Group lavas. These rocks, which include pillow lavas that formed when molten rock hit cold seawater, provide a rare glimpse into the Archean eon. The study suggests that water traveled deep beneath the surface to help form magma that fed volcanoes similar to those currently found in the Pacific “Ring of Fire.”
The Mechanism of “Dripduction”
In the modern era, water is moved into the mantle through subduction zones, where one rigid tectonic plate sinks beneath another. However, researchers state the early Earth was too hot for plates to behave in this manner, leaving it unclear how surface water could have reached the interior more than three billion years ago.
To explain this, the team proposes a geological mechanism called “dripduction.” According to the researchers, dense, water-rich sections of the cool outer crust would sporadically sag and collapse into the hotter mantle below. These collapsing pieces of crust carried water with them, which was then released into the mantle. This process created magmas that fed volcanic eruptions, as the intense heat turned the water into expanding steam.
The researchers describe this as gravity performing locally in short bursts what plate motion now achieves globally. Mass-balance calculations indicate that fluids released by this foundering crust supplied as much as 93 percent of certain trace elements in the mantle source that eventually melted to create the boninites.
Chemical Evidence in Ancient Lavas
The team focused on boninite, a rare, magnesium-heavy and water-rich lava. While boninites today erupt almost exclusively at plate boundaries where one plate grinds beneath another, the Whundo examples are the oldest extensive boninites known. By analyzing the chemical fingerprints of these rocks, the team estimated the water content of the mantle source.
Water lowers the melting point of mantle rock, similar to how salt turns ice to slush. The team’s calculations revealed the following water-by-weight comparisons:
- Whundo boninite mantle source: Between 0.8 and 1.5 percent water
- Present-day arc volcano mantle: Between 0.1 and 2 percent water
- Primitive mantle: Approximately 0.11 percent water
- Depleted mantle: Approximately 0.01 percent water
Because the ancient figures land squarely within the range of modern arc volcanoes, the researchers concluded that large amounts of water had already made their way deep into the interior. This pattern repeated across the sequence, suggesting the process continued for tens of millions of years.
Implications for Early Earth
The discovery addresses a fundamental geological question regarding when materials first began moving between the surface and the deep interior. This recycling process is critical because it influences the growth of continents, volcanic activity, and the movement of ingredients essential for life.
The study involved a collaboration between several institutions, including Adelaide University, Monash University, the Geological Survey of Western Australia, Curtin University, the Australian National University, Cardiff University, and the GEOMAR Helmholtz Center for Ocean Research in Germany.
While the findings suggest a dynamic young planet, the researchers noted that the study covers a single volcanic package of about 114 square kilometres. They acknowledged that arc-like volcanism from the Archean eon remains a subject of dispute regarding evidence for subduction.
