< h2 >你忘了大洲< / h2 >首先,有必要指出错误的前提下在你的问题:* *不正确的* *,“所有板块目前比白垩纪年轻”。有一个不间断的记录岩石拉伸一路回(阴间的)(https://en.wikipedia.org/wiki/Hadean) Eon 40亿年前。和年长的晶体称为(锆石)(https://en.wikipedia.org/wiki/Zircon) Radiometric_Dating年代发现夹杂物在老的岩石。问题是,这些岩石是在陆地上,(大陆地壳)(https://en.wikipedia.org/wiki/Continental_crust)的一部分。你的问题似乎没有意识到大陆地壳的存在。当然,因为你不是现在坐在大海的底部,你现在大陆地壳之上。大部分的大板块是海洋和大陆的一部分。大陆已经建立在地质时间一点点。他们的岩石是一个混乱的各种类型和年龄的拼图。这是地质学家的工作来找出这些部分如何组合在一起。 Here's just a taste, and it doesn't even show the complexity of the puzzle in North America by a long shot: ![basement rocks] (https://upload.wikimedia.org/wikipedia/commons/a/a7/North_america_basement_rocks.png) It is true that the oceanic plates are mostly destroyed by subduction, but the oceanic crust has to go beneath something, and there are complications: Subduction helps make continents grow. - not all of the rock is subducted: some seafloor sediments are scraped off and piled against continental margins - The top layers of rock that are subducted melt, and the melted rock bubbles its way up through the overlying crust, producing volcanic arcs. Sometimes these are on continents (such as the Cascades and Andes) so their rocks directly add mass to them. - When the volcanoes are out in the ocean, the subduction process pulls them into continents and they get cemented to the edge. Sometimes they form little mini- continents (such as Japan and New Zealand). The oldest oceanic crust currently at the seafloor is in the eastern Mediterranean, a remnant of the ancient Tethys Ocean during the Permian period, most oceanic crust is 200 million years old (Jurassic) or younger. They're an important part of putting the puzzle together, but as I stated at the beginning of my answer, the geological record is _much_ older, because of continental rocks. Finally, there is really old oceanic crust in the form of [ophiolites](https://en.wikipedia.org/wiki/Ophiolite), which are bits of oceanic crust that have been incorporated into continents. Since they're no longer part of the oceanic conveyor belt, some can be quite old. The oldest is about 3.8 billion years old.