A sex-linked trait is a trait that is carried by the X chromosomes in females but it is not expressed(the phenotype). Females are only carriers because they have two copies of the X chromosome [one of them carries the trait and the other does not]. Males who inherit one copy of the X chromosome often get the trait (because the trait is in either one copy or the other of the X chromosome) and express it while their Y chromosome would became recessive. Thus, only males express sex-linked traits such as hemophilia or color blindness
The sun heats the earth through radiation. Since there is no medium (like the gas in our atmosphere) in space, radiation is the primary way that heat travels in space. When the heat reaches the earth it warms the molecules of the atmosphere, and they warm other molecules and so on.