由于地球自转速率发生偏离，因此当把地球绕中轴旋转一圈作为一个单位时，（这种偏离）就相当于一秒钟时间。
Since Earth’s rotation rate varies, so would the value of one second when it’s defined as a fraction of the time it takes for one spin of the Earth on its axis.
线速度，在这个例子里，就是速率，是这个圆环的周长，除以走一圈，需要的秒数。
And that linear velocity, which, in this case, is really your speed, is of course the circumference of the circle divided by how many seconds it takes to go around.
在最近的地质历史中，气候变化的速率是史无前例的，它对地球生物圈产生了巨大的影响。
The rate of climate change could be unprecedented in the recent geologic history and have large effects on the terrestrial biosphere.
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