地球海底总是雕刻与我们今天所看到的许多地质特征?
绝对不是。海底板块构造在哪里开始和结束。海底非常动态和地球的年龄相比是非常年轻的。大部分的海底还不到2亿岁。非常古老的海洋地壳在地中海,这是只有约2.7亿岁。相比微不足道的4.5到46亿年地球已存在。
海洋地壳形成在大洋中脊和消失在俯冲带。这是什么使海洋动态地质条件。没有相应的大陆地壳的过程。大陆地壳一般是很古老的海洋地壳相比。
描述下面是一个从NOAA地图描绘了海洋地壳的年龄。注意,大洋中脊起着主导作用。
http://www.ngdc.noaa.gov/mgg/image/images/WorldCrustalAge.jpg
* *更新* *海底并不总是雕刻与我们今天所看到的许多地质特征。在本文(“间歇性板块构造?”*Science* 319.5859 (2008)](http://www.sciencemag.org/content/319/5859/85), Paul Silver and Mark Behn show that plate tectonics has come to a temporary standstill at times in the Earth's past. The deep ocean trenches that separate two continental plates on a collision course with one another disappear when those plates do collide. When this happened globally (e.g., the formation of a single supercontinent), the dominant slab-pull mechanism faltered, and that in turn shut down the mechanisms that form the mid-oceanic ridges. The mid-oceanic ridges slowly collapsed under their own weight. The end result was an ocean floor devoid of features.
这显然发生在盘古大陆的形成。大洋中脊的崩溃导致海平面大幅减少。海平面二叠纪末/三叠纪开始是300现在海平面以下400米。