Scientists tried to determine Earth’s age via our planet’s layers of rock, which must have been built over time.You’ve seen these rock layers if you’ve ever observed a cut-away section of a mountain, perhaps because a highway runs through it. In the early part of the 20th century, scientists still weren’t sure.
Taken as a whole, these data indicate that the Earth’s history extends backward from the present to at least 3.8 billion years into the past.
For example, scientists search for and date the oldest rocks exposed on Earth’s surface.
He concluded that Earth was born 20 to 400 million years ago.
Today’s scientists believe that answer is incorrect, but Kelvin’s calculations were in being based on logical thinking and mathematical calculation.
But rocks older than 3.5 billion years can be found on all continents.
Greenland boasts the Isua supracrustal rocks (3.7 to 3.8 billion years old), while rocks in Swaziland are 3.4 billion to 3.5 billion years.
In the early 20th century, scientists refined the process of radiometric dating.
Earlier research had shown that isotopes of some radioactive elements decay into other elements at a predictable rate.
But Earth’s layers of rock did not give up the secret of Earth’s age easily. However, from working with layer upon layer of rock laid down on Earth over long time spans, early 20th century scientists came to believe Earth not of atoms of one chemical element into another.
They led to the discovery that certain very heavy elements could decay into lighter elements – such as uranium decaying into lead.
As the dating technology progressed, these methods proved unreliable; for instance, the rise and fall of the ocean was shown to be an ever-changing process rather than a gradually declining one.