The ages of dinosaur fossils are determined by the layer of rock in which they are ... you can see the complete geologic column, how do scientists know it exists? ... laid down over 542 million years, for an average of 49,272 years per foot of rock. .... dinosaurs lived in shallow water because it would help support their weight
Some signs of a chemical change are a change in color and the formation of bubbles. The five conditions of chemical change: color change, formation of a precipitate, formation of a gas, odor change, temperature change.
Because Air itself is not an element. it is made up by different elements such as Oxygen and nitrogen. since its made up of a mix of different elements, its rather a homogeneous mixture :)
