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Long before I understood what any of it meant, I'd daydream in science class, staring at this chart, sounding out the names, wondering what those black-and-white bars meant, wondering what the colors meant, wondering why the divisions were so uneven, knowing it represented some kind of deep, meaningful, systematic organization of scientific knowledge, and hoping I'd have it all figured out one day.This all has to do with describing how long ago something happened. There are several ways we figure out relative ages.For example, isotopes with very long half lives are no good for dating rocks younger than about 100 million years.This is because, in just 100,000,000 years of time, not enough parent will have decayed for daughter concentrations to be reliably measured.
In the 1860's, English physicist Lord Kelvin disagreed with Charles Lyells proposition that the earth behaves in a uniform, unchanging manner.There are absolute ages and there are relative ages. We use a variety of laboratory techniques to figure out absolute ages of rocks, often having to do with the known rates of decay of radioactive elements into detectable daughter products.Unfortunately, those methods don't work on all rocks, and they don't work at all if you don't have rocks in the laboratory to age-date. They are descriptions of how one rock or event is older or younger than another.Mountains, erosion, and variations in climate were considered to be punishment for the sins committed by humanity.
Buffon's Iron Sphere Experiments- On the basis of iron sphere cooling experiments, Frenchman Georges de Buffon estimated that the Earth would have needed 75,000 years to cool to its present temperature.
Led by Dr George Nash, archaeologist and specialist in prehistoric and contemporary art, Erasmus Mundus Professor of the Polytechnic Institute of Tomar, convener of the Welsh Rock Art Organisation and Research Fellow, Dept.