Volcanic ash used dating fossils

The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata. Such index fossils must be distinctive, globally distributed, and occupy a short time range to be useful.Misleading results can occur if the index fossils are incorrectly dated.In addition, the oldest known moon rocks are 4.5 billion years old.Since the moon and the Earth probably formed at the same time, this supports the current idea of the Earth's age.Other techniques include analyzing amino acids and measuring changes in an object's magnetic field.

Radiometric dating isn't the only method of determining the age of rocks.

Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.

Unfortunately, these elements don't exist in dinosaur fossils themselves.

Family-tree relationships can help to narrow down the date when lineages first appeared.

For example, if fossils of B date to X million years ago and the calculated “family tree” says A was an ancestor of B, then A must have evolved earlier.

Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution.

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