Life is well over 3.5 billion years old, and until about 600 million years ago, the planet was dominated by microbes.
Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.
As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.
Darwin had finally gotten the luxury of time he had craved.
The dates that radioactive clocks have put on evolutionary history are astonishing.
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).He came up with that figure by estimating how long it had taken for the planet to cool down to its current temperature from its molten infancy.But Kelvin didn't, and couldn't, know that radioactive atoms such as uranium were breaking down and keeping the planet warmer than it would be otherwise. And we talk about the word isotope in the chemistry playlist. But this number up here can change depending on the number of neutrons you have. And every now and then-- and let's just be clear-- this isn't like a typical reaction. So instead of seven protons we now have six protons. And a proton that's just flying around, you could call that hydrogen 1. If it doesn't gain an electron, it's just a hydrogen ion, a positive ion, either way, or a hydrogen nucleus. And so this carbon-14, it's constantly being formed. I've just explained a mechanism where some of our body, even though carbon-12 is the most common isotope, some of our body, while we're living, gets made up of this carbon-14 thing. So carbon by definition has six protons, but the typical isotope, the most common isotope of carbon is carbon-12. And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oceans. When people talk about carbon fixation, they're really talking about using mainly light energy from the sun to take gaseous carbon and turn it into actual kind of organic tissue.So the rate at which this happens, so the rate of carbon-14 decay, is essentially half disappears, half gone, in roughly 5,730 years. Even better, maybe you dig a little deeper, and you find another bone. And you say, wow, you know this thing right over here has 1/4 the carbon-14 that I would expect to find in something living. Well, if it only has 1/4 the carbon-14 it must have gone through two half lives.