科学美国人60秒 SSS 地球磁极倒转历时数千年

（单词翻译）

This is Scientific American's 60-second Science, I'm Annie Sneed.

Earth's magnetic field—which creates our planet's north and south pole—is far from fixed¹. In fact, the field is quite active; sometimes it weakens, and even reverses, causing Earth's polarity to switch. Reversals don't happen very often, though—only about every 100,000 to million years. That's part of why this phenomenon has largely remained a mystery for scientists. However, a recent study may help researchers better understand how long and how complicated Earth's magnetic field reversals really are.

The last polarity reversal took place some 770,000 years ago. In a new study, researchers used lava² flow records, along with sedimentary and Antarctic ice core data, to examine that event. They found that the reversal took about as long as many scientists previously³ believed it did—just a few thousand years.

But the researchers also examined the period prior to that final reversal process. And they discovered that a lot was happening with Earth's magnetic field thousands of years beforehand.

"There's clear evidence from the volcanic⁴ rocks of a major excursion happening at about 795,000 years ago."

Brad Singer, a geoscientist at the University of Wisconsin, Madison, who led the study.

"And that was followed by another excursion, which is the unexpected finding of this study, at about 784,000... The two excursions that we've discovered in the lava record, and are seen in some of the sedimentary records, are a sign that the dynamo is beginning to undergo the reversal process 20,000 years earlier than the final reversal took place. So our arguments would be that the reversal process is complicated and long-lived, and it gets underway, it gets initiated⁵ well before the final reversal takes place."

All this activity prior to the final reversal is vital for our grasp of the process.

"The ultimate goal here is, we want to understand what drives reversals—what really happens in the dynamo? And if you just start and look at this short period right around the reversal, you're missing all this unusual behavior that happens in thousands of years prior to that."

We need to know if Singer's findings hold true for magnetic field reversals in general. Alterations⁶ in the field will mess with critical human systems, such as the GPS satellites that help us navigate⁷. Fortunately, whenever the next reversal happens, it looks like we'll have plenty of time to prepare.

Thanks for listening for Scientific American — 60-Second Science. I'm Annie Sneed.

这里是科学美国人——60秒科学系列，我是安妮·斯尼德。

地球磁场创造了地球的南北两极，但它可不是固定不变的。事实上，磁场相当活跃；它有时会变弱，甚至逆转，导致地球两极反转。不过这种反转不常发生，大约每10万到100万年才会发生一次。这就是这种现象在很大程度上对科学家来说仍是个谜的部分原因。然而，最近的一项研究可能有助于研究人员更好地理解地球磁场反转究竟持续了多长时间以及到底有多复杂。

最近一次地磁极性倒转发生在大约77万年前。在一项新研究中，研究人员用熔岩流记录以及沉积物和南极冰芯数据来研究这一事件。他们发现，磁极倒转所需时间与许多科学家之前认为的一样长——只需要几千年。

但研究人员还研究了最后一次倒转过程发生前的那段时期。他们发现，在之前的数千年里，地球磁场发生了很多变化。

“来自火山岩的明确证据表明，磁极在大约79.5万年前发生过一次大偏移。”

领导这项研究的威斯康星大学麦迪逊分校的地球学家布拉德·辛格说到。

之后在大约78.4万年前又发生过一次偏移，这是这项研究的意外发现。我们在熔岩记录和某些沉积物记录中发现的两次偏移是一种迹象，表明动力场开始经历反转过程的时间比最后一次磁极倒转发生的时间早了2万年。因此我们的论点是，这一反转过程复杂而长久，早在磁极最终倒转发生前就开始了。

最终倒转发生之前的所有活动对我们理解这一进程至关重要。

“最终目标是，我们想知道是什么驱动了磁极反转——动力场内到底发生了什么？如果你只观察反转前后的短期情况，你就会错过此前数千年间发生的所有这些异常行为。”

我们需要知道辛格的研究结果是否适用于一般的磁场反转。磁场变化会干扰重要的人类系统，比如帮助我们导航的GPS卫星。幸运的是，无论下一次反转何时发生，看起来我们都有充足的时间做准备。

谢谢大家收听科学美国人——60秒科学。我是安妮·斯尼德。