Radioactivity Heats Things Up

After Alfred Wegener's death in 1930, much of the controversy over continental drift began to die down. Most scientists felt that there were just too many flaws in the theory to give it much serious consideration. Rather than pursue it further, they went about their business conducting research in other areas of geology. Nevertheless, Wegener's ideas did not completely die out.

In South Africa, a geologist named Alexander Du Toit firmly believed that Wegener's reconstruction of Pangaea was correct. He continued working on the problem after Wegener's death and produced even more evidence to show that connections between the continents had existed in the past. In Switzerland, another geologist named Emile Argand was convinced that continental drift was the best way to explain the formation of mountains like the Alps. Argand's field work led him to conclude that the huge folds of rocks found in the mountains could only be produced by continents smashing together.

Unfortunately, the biggest question about the theory still went unanswered: What type of force could actually move something the size of a continent through the Earth? The answer would be found thanks to a newly discovered energy source called radioactivity. Not only would radioactivity provide the means for making conti-

Layers Cliff
Figure 3.1 The folded strata, or rock layers, are visible in the horizontal bands along this cliff face in Austria. The folds provide evidence of tectonic forces pushing against each other in the Earth's crust.

nents move, but it would also provide an "atomic clock" that would finally allow scientists to determine an age for Earth.

Back in 1896, a French physicist named Henri Becquerel made an astonishing discovery. He was conducting studies on a newly discovered form of energy called the X-ray and trying to find out whether these mysterious rays were produced by any natural materials. He had stored a container filled with salts of the element uranium in a desk drawer along with some new photographic plates. When he retrieved the plates, he found that they had somehow been exposed. When he developed the plates, he found they contained images of the uranium salt crystals— some invisible energy source from the salt crystals was causing changes in the plates. Two years later, Marie and Pierre Curie came up with a name for this mysterious phenomena: radioactivity. The energy that came from these special materials was called radiation.

During their research, the Curies discovered that many naturally occurring minerals typically found in the Earth are radioactive. When these minerals release their radiation, they also release heat. (It is this heat from radioactive elements that engineers use in modern-day nuclear power plants to make steam to generate electricity.)

Picking up where the Curies left off, an English physicist named Ernest Rutherford made another amazing discovery. Scientists had long believed that atoms were the smallest particle that matter could be divided into. They also believed that atoms themselves could not change. An atom of oxygen would always stay an atom of oxygen, and an atom of carbon would always be carbon. Rutherford found that this was not always the case. Atoms of radioactive elements did change: Over time, uranium atoms would turn into atoms of lead, a process that took place in a very predictable way.

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