Stixrude Lars, Scipioni Roberto, Desjarlais Michael P
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, 90095, USA.
Department of Earth Sciences, University College London, London, WC1E 6BT, UK.
Nat Commun. 2020 Feb 25;11(1):935. doi: 10.1038/s41467-020-14773-4.
The Earth's magnetic field has operated for at least 3.4 billion years, yet how the ancient field was produced is still unknown. The core in the early Earth was surrounded by a molten silicate layer, a basal magma ocean that may have survived for more than one billion years. Here we use density functional theory-based molecular dynamics simulations to predict the electrical conductivity of silicate liquid at the conditions of the basal magma ocean: 100-140 GPa, and 4000-6000 K. We find that the electrical conductivity exceeds 10,000 S/m, more than 100 times that measured in silicate liquids at low pressure and temperature. The magnetic Reynolds number computed from our results exceeds the threshold for dynamo activity and the magnetic field strength is similar to that observed in the Archean paleomagnetic record. We therefore conclude that the Archean field was produced by the basal magma ocean.
地球磁场已经运作了至少34亿年，然而古代磁场是如何产生的仍然未知。早期地球的地核被一层熔融的硅酸盐层包围着，这是一个可能存续了超过10亿年的基性岩浆海洋。在这里，我们使用基于密度泛函理论的分子动力学模拟来预测基性岩浆海洋条件下（100 - 140吉帕斯卡，4000 - 6000开尔文）硅酸盐液体的电导率。我们发现，电导率超过10000 S/m，比在低压和低温下测量的硅酸盐液体的电导率高出100多倍。根据我们的结果计算出的磁雷诺数超过了发电机活动的阈值，并且磁场强度与太古宙古地磁记录中观测到的相似。因此，我们得出结论，太古宙磁场是由基性岩浆海洋产生的。
