Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
The Conflict Over the Sovereignty of the Diaoyu Islands -- between Taiwan (ROC), China (PRC), & Japan depth of the Okinawa trough that locates in the east is as deep as 2,717 meters, forming a natural sea boundary with China and the Ryukyu islands. As the geological structure of the Ryukyu Islands belong to "oceanic crust", the Diaoyu Islands are "continental crust" that makes a significant difference in between those two. Also, the Diaoyu Islands has one of the largest scale of continental reef layer that contains an abundant amount of river deposits such as the Yangtze River and the Yellow River, and is therefore potentially rich in oil. The Diaoyu islands are considerably much more strategic