Rocks from around the world have been dated using this method, including the older volcanoes in the Galápagos Islands.Scientists have also dated rocks from central Africa that contain fossil evidence of the first human species.Yet other Galápagos lava flows are as young as a few hundred years.
We make use of cosmic rays that come from deep space and are constantly hitting the Earth.
When they hit, they produce tiny amounts of different elements in rock surfaces by nuclear reactions. Just like natural radioactivity, if we know the rate of production of helium-3 and we can measure how much is produced by the cosmic rays, we can calculate how long the rock has been exposed on the surface of the Earth.
Imagine the sand in the top is a group of parent elements.
The grains move through the narrow part of the hourglass at a constant rate.
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The reliably dated lavas from Loihi are from a 500 m thick section on the east flank of the volcano and they range in age from 5 ± 4 to 102 ± 13 ka.
These lavas are all alkalic and are from the preshield stage of volcanism.
When they fall into the bottom, they have changed into daughter elements.