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Jun. 24th, 2014 10:56 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
pustomytnyk„Just over a century ago, it was still widely believed that the Sun may have formed as recently as 20 million years ago, because if you waited much longer, the loss of energy radiated away as sunshine would have caused gravity to compress it to a much smaller size than we observe. Similarly, it was calculated that if one waited much longer than that, most of Earth’s inner heat (manifested as volcanoes and geothermal vents) would cool away.
The mystery of what keeps the Sun warm wasn’t solved until the 1930s when nuclear fusion was discovered. But before then, the 1896 discovery of radioactivity demolished the old estimates of Earth’s age and also provided a great method for making better ones. The most common isotope of uranium atoms spontaneously decays into thorium and other lighter atoms at such a rate that half of the atoms have fallen apart after 4.47 billion years. Such radioactive decays generate enough heat to keep Earth’s core nice and toasty for billions of years, explaining why Earth is so warm even if it’s way older than 20 million years.“
The mystery of what keeps the Sun warm wasn’t solved until the 1930s when nuclear fusion was discovered. But before then, the 1896 discovery of radioactivity demolished the old estimates of Earth’s age and also provided a great method for making better ones. The most common isotope of uranium atoms spontaneously decays into thorium and other lighter atoms at such a rate that half of the atoms have fallen apart after 4.47 billion years. Such radioactive decays generate enough heat to keep Earth’s core nice and toasty for billions of years, explaining why Earth is so warm even if it’s way older than 20 million years.“
