Strata are differentiated from each other by their different colors or compositions and are exposed in cliffs, quarries, and river banks.

These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top.

These long time periods are computed by measuring the ratio of daughter to parent substance in a rock and inferring an age based on this ratio.

Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios.If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent.All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Models are unreliable "[Models] are full of fudge factors that are fitted to the existing climate, so the models more or less agree with the observed data.Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. But there is no reason to believe that the same fudge factors would give the right behaviour in a world with different chemistry, for example in a world with increased CO2 in the atmosphere." (Freeman Dyson)Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice – and the sun.