Age of the Earth
Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
The Earth formed about 4.6 billion years ago (4,600 million years), or 4.54 billion years ago to be more exact. Scientists find this age by radiometric dating. This method measures the steady decay of radioactive elements in meteorites and in the oldest Earth minerals. At first the Earth was hot, barren and rocky, with a thin atmosphere of hydrogen and helium.
Example
Tiny zircon crystals from Jack Hills, Western Australia, are about 4.4 billion years old. They are the oldest known pieces of the Earth.
Don't confuse with
- Age of the universe: the universe began with the Big Bang about 13.8 billion years ago (NCERT: 13.7). That is about three times older than the Earth.
- Age of the oceans: the oceans formed later, within 500 million years of the Earth's birth, so they are about 4,000 million years old.