The notion is that people have failed to detect the massive changes which have happened in the ocean because they have been looking back only a relatively short time into the past.
【词汇突破】 detect ：检测，侦查
massive：巨大的，大规模的（写作中可用到的替换词）
【主干识别】The notion is that 加表语从句
【其他成分】people have failed to detect the massive changes 表语从句（表语从句是对主语的阐释。）；which have happened in the ocean 定语从句，修饰为changes；because they have been looking back only a relatively short time into the past原因状语从句。
【微观解析】句子的主干是The notion is that+表语从句，而定语从句则是修饰表语从句中的一个词，因此在理解翻译时需要注意主次关系。对于fail这一类带有否定意味的词可直接作为not来理解。relatively 修饰short .
【难点揭秘】原句中的从句较多，需要有层次的去理解，
【译文赏析】意思就是说人们没有发现海里发生的巨大变化，因为他们只看了过去相对较短的一段时间。
【翻译点拨】对于The notion is的处理可以是 意思是说,或者，人们认为