Age of the Earth research. Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics, weathering and hydrothermal circulation. All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide (a species of atom characterised by the number
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