Radiometric dating evolution
At the dawn of the twentieth century, physicists made a revolutionary discovery: elements are not eternal.
Atoms can fuse together to create new elements; they can also spontaneously break down, firing off subatomic particles and switching from one element to another in the process (see figure, right).
While some physicists used these discoveries for applications ranging from nuclear weapons to nuclear medicine, others applied them to understanding the natural world.
The sun was once thought to burn like a coal fire, but physicists showed that it actually generates energy by slamming atoms together and creating new elements.
Life is well over 3.5 billion years old, and until about 600 million years ago, the planet was dominated by microbes.
Radioactive clocks have shown that evolution can change its pace the Cambrian Explosion of about 535 million years ago saw the relatively rapid emergence of many major lineages of animals in just a few million years.
When Rutherford announced his findings it soon became clear that Earth is millions of years old.
These scientists and many more after them discovered that atoms of uranium, radium and several other radioactive materials are unstable and disintegrate spontaneously and consistently forming atoms of different elements and emitting radiation, a form of energy in the process.
In 1956 the American geologist Clair Patterson (left) announced that the Earth was 4.5 billion years old.
Nineteenth century geologists recognized that rocks formed slowly as mountains eroded and sediments settled on the ocean floor.
But they could not say just how long such processes had taken, and thus how old their fossils were.
Willard Libby and his colleague Ernest Anderson showed that collected from sewage works had measurable radiocarbon activity whereas methane produced from petroleum did not.
Perseverance over three years of secret research to develop the radiocarbon method came into fruition and in 1960 Libby received the Nobel Prize for chemistry for turning his vision into an invaluable tool.