How Old is Earth?
Measurements made in the 18th century were based on the rate of the Earth's cooling and vastly underestimated the age of the Earth to be in the hundreds of thousands of years.
Later guesses by esteemed scientists like Charles Darwin (who proposed 306.7 million years) and Lord Kelvin (who made several erroneous proposals spanning hundreds of millions of years) were moderate improvements.
The ability to accurately date our planet — which formed out of debris left behind by the birth of the sun — developed with the understanding of radioactive decay. Radioactive substances release subatomic particles at a very steady rate. Sometimes the age of an object can be determined by comparing present amounts of a radioactive substance with the supposed original amount in the object. Uranium is a particularly well-understood, naturally radioactive element. By measuring lead to uranium ratios in ancient rock samples, in 1953 scientists deftly put Earth's age at 4.5 to 4.6 billion years, an estimate that stands today.
Life's Little Mysteries: Gift Edition Hardcover Book
Uncover the truth behind more than 100 mysteries that surround us every day with our new hardcover book! Perfect for gifts and classrooms, and suitable for all ages. Some of the included mysteries are:
- Why Do Cats Land on Their Feet?
- How Long Does it Take to Make Petrified Wood?
- What Everyday Things Around Us Are Radioactive?
Find out all of this and much, much more in our NEW hardcover book.
It makes a great gift idea for all ages. more info>>