It is not surprising, therefore, that the highest ratio of oil and gas pools to volume of sediment is found in rock no older than 2.5 million years—young enough so that little of the petroleum has leaked away—and that nearly 60 percent of all oil and gas discovered so far has been found in strata that formed in the last 65 million years. (TPO43, 65)

大家自己先读，不回读，看一遍是否能理解

托福阅读长难句分析：

It is not surprising,therefore, (that the highest ratio of oil and gas pools to volume of sediment is found in rock no older than 2.5 million years)—young enough so that little of the petroleum has leaked away—and (that nearly 60 percent of all oil and gas discovered so far has been found in strata that formed in the last 65 million years). (TPO43, 65)

这个句子的结构：

It is not surprising that 从句 and that 从句

主要就是两个从句，然后中间有一个破折号隔开

修饰一：(that the highest ratio of oil and gas pools to volume of sediment is found in rock no older than 2.5 million years)，从句

中文：油藏和气藏的数量与沉积物总量的比率最高出现在年龄不超过250万年的岩石中

修饰二：(that nearly 60 percent of all oil and gas discovered so far has been found in strata that formed in the last 65million years)，从句

大家注意，能不能来理解这个从句中的discovered?先想想看。

其实，这个句子中还有一个非谓语动词修饰成分，that nearly 60 percent of all oil and gas (discoveredso far) has been found in strata that formed in the last 65 million years

中文：约60%的石油和天然气都被发现在过去650万年形成的岩层中

托福阅读长难句参考翻译：

因此，毫无意外，油藏和气藏的数量与沉积物总量的比率最高出现在年龄不超过250万年的岩石中——岩石还很新，以至于很少的石油泄露——而目前为止发现的约60%的石油和天然气都被发现在过去650万年形成的岩层中。

这个句子的主要修饰成分就是从句和非谓语动词，大家务必想清楚，每一个修饰成分修饰的是什么，才能看清楚这个句子的结构。