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 Dog and Its Reflection down as it is crossing a stream and sees its own reflection in the water. Taking it for another dog carrying something better, it opens its mouth to bark at the "other" and in doing so drops what it was carrying. The story became incorporated into mediaeval animal lore. The Aberdeen Bestiary, written and illuminated in England around 1200, asserts that 'If a dog swims across a river carrying a piece of meat or anything of that sort in its mouth, and sees its shadow, it opens its mouth and in hastening to seize the other piece of meat, it