A new study conducted by Professor Masaki Yoshida from Ritsumeikan University, published on July 6, 2026, reveals that the Earth's deepest rocks define a geophysically significant upper limit for viscosity. This research integrates various data sources to suggest that the upper bound of viscosity is approximately 1030±2 Pa s, marking the threshold where materials transition from deformable flow to rigid behavior over geological timescales.
Understanding Viscosity and Its Upper Limits
Viscosity is a fundamental property that describes how materials flow, influencing the movement of liquids and molten rocks, as well as regions deep within the Earth. While low and moderate viscosities have been extensively studied, the question of whether there exists a meaningful upper limit to viscosity has remained largely unanswered.
To explore this, Yoshida's study investigated the Earth's interior as a natural constraint on viscosity over finite timescales. The research combined geodetic observations, laboratory experiments on rock deformation, and numerical simulations to derive a comprehensive understanding of viscosity limits.
Key Findings from the Research
The study identified three main lines of evidence to support its findings:
- Geodetic observations indicate stable tectonic plates exhibit effective viscosities of approximately 1024 Pa s or greater.
- Laboratory experiments on major rock-forming minerals, including olivine and quartz, were conducted under realistic temperature and pressure conditions.
- Numerical simulations analyzed how highly viscous lithospheres behave during tectonic activities such as plate motion and subduction.
These independent approaches converged on a similar viscosity range, reinforcing the study's conclusions regarding the upper limit of viscosity.
The Implications of Viscosity Limits
The proposed upper bound of 1030±2 Pa s suggests that materials with such high viscosities effectively behave as rigid bodies over geological timescales. For comparison, water has a viscosity of approximately 10-3 Pa s, making the upper limit roughly 1033 times greater than that of water.
Yoshida emphasized, "This study suggests that the upper bound of viscosity is 1030±2 Pa s, based on the physical definition of viscosity as resistance to flow over finite timescales, from human-observable to Earth-history timescales." This research not only impacts the field of geophysics but also provides insights into high-viscosity non-Newtonian fluids and glassy materials.
🤖 This article was rewritten by Feed and Figures' editorial AI from a report originally published by Phys.org. Facts and quotes are preserved from the original; the rewrite focuses on clarity and structure. For the unedited original, see the source link below.
