What evidence, observation and method have scientists used to determine the age of the earth?

Question

Pysical Geography Question:
What evidence, observation and method have scientists used to determine the age of the earth?

Answer 1

Scientists have stated over the years that the Earth's age is ____ years old.

Many times this number has changed, and each time they have said that they have "proof" that the Earth is so many million (now they say "billion") years old.

The problem with the dating methods is that they rely on a certain set of assumptions that cannot be themselves proven.

Among these are
1. the initial condition of the rock samples are assumed to be known.
2. "Aging" is assumed to occur at a constant rate.
3. The ratio of the elements in the rocks tested has not been altered by processes other than radioactive decay.

Many of the dating methods give contradictory results.

For example, new rock formed by the Mount St. Helens erruption was tested and the Potassium-Argon dating method indicated it was between 0.5 and 2.8 million years old! Other examples have also dated things that were known to be young as very old.

The problem is there is no way to accurately test the dating methods, therefore, at best we do not know if they are correct or not in most cases!

Answer 2

The mid ocean ridge. It's a crack in the bottom of the ocean that magma pours out of occasionally. The earth's magnetic poles switch every couple hundred thousand years, so the bits of iron in the long cooled volcanic rock(along the mid ocean ridge) line up towards the magnetic poles. When the poles switch, the iron on the new rock lines up in a new direction.
Scientists take samples from the ocean floor and count how many times the poles switched and uses the information to make a approximated guess on how old the earth is.
Hope that helps!

Answer 3

Radioactive decay of certain elements in crystals.