五亿多年来，地球磁场强度与大气含氧量始终同步波动，科学家终揭开其中奥秘。美国国家航空航天局主导的研究揭示了地球深部过程与地表生命活动间存在显著关联：行星内部翻腾的熔融物质可能正微妙塑造着生命存续条件。通过比对古地磁记录与大气数据，研究人员发现自寒武纪生命大爆发（复杂生命首次繁荣时期）以来，这两种看似无关的现象始终保持着同步变化。这一诱人关联暗示着某种单一隐藏机制——或许连大陆漂移也参与其中——在协同调控磁力强度与人类呼吸的空气。
Earth's magnetic field arises from the flow of material in the planet's molten interior, which acts like a giant electromagnet. The flow isn't perfectly stable, and this causes the field to change over time.
Many scientists have argued that the magnetic field is crucial for protecting the atmosphere from eroded by energetic particles coming from the Sun. But, the authors of the study in Science Advances point out, the role of magnetic fields in preserving the atmosphere is an area of active research. Before addressing the complexity of the cause-and-effect relationship between magnetic fields and oxygen levels, the study authors decided to see whether Earth's magnetic field and atmosphere have fluctuated in ways that demonstrate a link.
The history of the Earth's magnetic fields is recorded in magnetized minerals. When hot minerals that rise with magma at gaps between spreading tectonic plates cool down, they can record the surrounding magnetic field. The minerals retain the field record as long as they are not reheated too severely. Scientists can deduce historic oxygen levels from ancient rocks and minerals because their chemical contents depend on the amount of oxygen available when they were formed. Data for both Earth's magnetic field and oxygen extend over comparable ranges in databases that myriad geophysicists and geochemists have compiled. Until now, the authors of the new study say, no scientists had made a detailed comparison of the records.
"These two datasets are very similar," said coauthor Weijia Kuang, a geophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Earth is the only known planet that supports complex life. The correlations we've found could help us to understand how life evolves and how it's connected to the interior processes of the planet."
When Kuang and colleagues analyzed the two separate datasets, they found that the planetary magnetic field has followed similar rising and falling patterns as oxygen in the atmosphere for nearly a half billion years, dating back to the Cambrian explosion, when complex life on Earth emerged.
"This correlation raises the possibility that both the magnetic field strength and the atmospheric oxygen level are responding to a single underlying process, such as the movement of Earth's continents," said study coauthor Benjamin Mills, a biogeochemist at the University of Leeds.
The researchers hope to examine longer datasets to see if the correlation extends farther back in time. They also plan to investigate the historic abundance of other chemicals essential for life as we know it, such as nitrogen, to determine whether they also support these patterns. As for the specific causes linking the Earth's deep interior to life on the surface, Kopparapu said: "There's more work to be done to figure that out."