Ozone layer upper-atmosphere ozone-depletion rate slowed down significantly during the previous decade. Some breakdown can be expected to continue because of ODSs used by nations which have not banned them, and because of gases which are already in the stratosphere. Some ODSs, including CFCs, have very long atmospheric lifetimes, ranging from 50 to over 100 years. It has been estimated that the ozone layer will recover to 1980 levels near the middle of the 21st century. A gradual trend toward "healing" was reported in 2016. Compounds containing C–H bonds (such as hydrochlorofluorocarbons, or HCFCs) have been designed to replace CFCs in certain
Layer by Layer starts by making a cross on one face with the edge pieces, then putting the corners into position between the edges. By then the layer should be solved. Third, the four edge pieces of the middle layer are solved. At this point the first two layers are solved. Fourth, a cross of the opposite color is made on the last layer. Fifth, the last layer edges are permutated (swapped around). Sixth, the last layer corners are permutated. Finally, the last layer corners are oriented. Most Layer by Layer beginners' methods solve the first two layers using the same technique. However,