Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA.
Science. 2010 Mar 5;327(5970):1238-40. doi: 10.1126/science.1183445.
Stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss. Although the early Earth retained its water and atmosphere, and thus evolved as a habitable planet, little is known about Earth's magnetic field strength during that time. We report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3.4 to 3.45 billion years ago. The measured field strength is approximately 50 to 70% that of the present-day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of < or = 5 Earth radii, similar to values observed during recent coronal mass ejection events. The data also suggest lower-latitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition.
恒星风被行星磁场阻挡，防止大气侵蚀和水分流失。尽管早期地球保留了水和大气，从而演化为宜居行星，但人们对当时地球磁场强度知之甚少。我们报告了来自含有磁性包裹体的单一硅酸盐晶体的古强度结果，这些晶体记录了 34 亿至 34.5 亿年前的地球发电机。测量到的场强大约是目前场强的 50%至 70%。当与更大的古太古代太阳风压力结合时，古场强数据表明稳定状态磁层顶的阻挡距离<或=5 个地球半径，类似于最近日冕物质抛射事件中观察到的值。这些数据还表明，低纬度极光和极区帽面积增加，以及来自外逸层的加热、膨胀和挥发性损失，这将影响长期大气成分。
