科学美国人60秒 SSS 影响地球的不止是太阳和月亮

Jupiter and Venus Squeeze Earth's Orbit

The Sun exerts an enormous and obvious influence on the Earth, with its gravity and light. But other bodies also have a small say in our affairs.

太阳用其重力和光线对地球产生巨大而明显的影响。但其他天体对地球也会产生轻微的影响。

"We're not alone in the solar system, there are other planets.” Dennis Kent, a geologist 1 at Rutgers University, and Columbia's Lamont-Doherty Earth Observatory 2. "And as we circle the sun, those other planets and also our moon exert effects on our orbit."

“罗德斯大学的地质学家Dennis Kent和哥伦比亚大学的Lamont-Doherty Earth Observatory表示：“我们并不孤单，太阳系中还有其他行星。当我们绕太阳转时，那些其他星球以及月球也在影响我们的轨道。”

In fact, planetary scientists have long hypothesized that Venus and Jupiter squeeze the Earth's orbit from circular to elliptical and back every 405 thousand years. During an elliptical orbit, when the distance from the sun varies more, the differences between the seasons would be more extreme than when the orbit is virtually circular. Problem is, it's been hard to verify that this oscillation between orbit shapes exists.

事实上，行星科学家很早就假设，金星和木星将地球的轨道，从圆形轨道挤压到椭圆形轨道，并且每40.5万年回归一次。在椭圆轨道中，当与太阳的距离变化更大时，季节之间的差异，将比轨道几乎是圆形时更为极端。那么问题是，很难验证这种轨道形状之间的振荡是否存在。

But Kent and his colleagues came up with a way—by boring down into the Earth. They took a rock core from the east coast, which has excellent sediment 3 records—good evidence of extreme seasonal 4 variations. They compared that core with another from Arizona, embedded 5 with zircons. The zircons contain trace amounts of uranium, which decays in a predictable way—meaning the Arizona core could thus be dated based on uranium content.

但Kent和他的同事，想出了一条通往地球的道路。他们从东海岸采集了一块岩芯，这块岩芯具有极好的沉积物记录——季节变化的良好证据。他们将这个岩芯与来自亚利桑那州的另一个岩芯，进行了比较并嵌入了锆石。锆石中含有微量的铀，这种铀以可预测的方式衰变——这意味着，亚利桑那核心可以基于铀含量进行研究。

Magnetic information in both cores allowed them to be lined up—and the Arizona dates then provided a time-line for the ancient floods and droughts embedded in the east coast core.

两个岩芯中的磁性信息，使得它们排列整齐—亚利桑那日期，为东海岸核心中埋藏的古代洪水和干旱提供了时间线。

And all that evidence confirmed the mathematical simulations: Jupiter and Venus do push us around, and thus slowly alter our orbit over hundreds of millennia 6. The details are in the Proceedings 7 of the National Academy of Sciences.

所有这些证据都证实了数学模拟试验结果：木星和金星确实在推动着地球，并因此在数千年的时间里，缓慢地改变了我们的轨道。该研究结果发表在《美国国家科学院》杂志。

Kent says the discovery also provides a new way to interpret the history of life on the planet. "It's a clock. And so being able to have a precise chronometer 8 we can relate things like speciation events, or dispersals of various life forms. It allows us to look at these things and try to understand what's driving them."

As for whether modern-day humans need to worry about this 405 thousand year oscillation?

Kent说，这一发现还为解释这个星球上的生命史，提供了一种新的方式。“这是一个时钟，所以能够拥有一个精确的计时表，我们可以将事物与物种形态事件，或各种生命形式的分散联系起来，它使我们能够观察这些事物，并试图了解是什么驱使它们。那么现代人类是否需要担心这个40.5万年的振荡?

"This is probably pretty low down the list of things to be concerned about. How much CO2 we're putting in the atmosphere, that's of a more immediate 9 concern." Because, despite our planetary neighbors’ best efforts, our orbit has barely budged 10 as we’ve observed our climate change.

“这可能是相当低概率的事情，需要关注的事情很多，我们在大气中投入了多少二氧化碳，这是一个更直接的问题。”因为尽管我们周围的邻居们，尽了最大的努力，但我们的轨道，在我们观察到气候变化时几乎没有变化。