有个问题~~~ 请英语高手 帮我解答下~~~是关于英语语法的问题！

在过去的几个百万年，地球的气候实际上一直默认为冰河时代。

over the past several million years ， over 可以翻译为“在“的意思，一般后面用现在完成时。

个人认为“for”其实可以省略，如果在这里，可以认为是“对……而言”。即
【对】在过去的几个百万年【而言】，地球的气候实际上一直默认为冰河时代。

Professor I’d like to take you back about 11 thousand years ago when Earth entered the latest interglacial period. Interglacial periods are, typically periods of time between Ice Ages, when the climate warms, and the glacial ice retreats for a time, before things cool off again and another Ice Age begins. And for over the past several million years, Earth’s sort of default climate has actually been Ice Age, but we have experienced periodic regular thaws, and the last one, the one we are in now, started about 11 thousand years ago.
答：我认为这里的for与over是重复使用。用其中的任何一个都可以：
For the past several million years, Earth’s sort of default climate has actually been Ice Age
Over the past several million years, Earth’s sort of default climate has actually been Ice Age
介词over还可以改为In, during
In/During/Over/For the past/last several million/ 50/ thousand/... years, 作时间状语，主句谓语用现在完成时。
见过双介词from behind, in between 吗？ 我认为这属于双介词，相当于for and over 的省略and

for与over后跟一段时间，其实还是有一点差别的。for可以说是一条直线，over是一条弧线。for ten years, ------------>, over ten years, ...;;;;;;''''''````;;;;;;;......> 象一条平抛线那样的，有跨越之意。

for over the past several million years --> for (over the past several million years)

over the years 固定搭配
over the past several million years：在过去的百万年间里

简单点，你就看成 for the past several million years 好了。over只是强调在那个entire时间段之内都怎么样怎么样。

for 后接表示一段的时间，而over在数字前一般表示超过，多于，相当于more than,，所有，逗号前的那个是整个这句话的时间状语，意思是，经过了过去几百多万的时间