Potassium dating rocks

Thus, radioactive decay of samarium was faster than that of rubidium, which was faster than that of potassium.

Such accelerated radioactive decay rates would mean that these basalt lavas may instead be only thousands of years old.

This is then said to be the rock’s exact (or absolute) age.

These radioactive dating methods have been used to calculate an absolute age of 1,103±66 million years for the Cardenas Basalt lavas.

This is identical to the rubidium-strontium isochron age of 1,111±81 million years for the Cardenas Basalt lavas near the bottom of Grand Canyon strata sequence So how can the youngest basalt lava flows in Grand Canyon, whose eruption was possibly witnessed only thousands of years ago, yield the same radioactive rubidium-strontium age of 1.1 billion years as some of the oldest basalt lava flows at the bottom of the Canyon?

Answer: The molten rock that produced the young basalt lava flows came from deep inside the earth, from what geologists call the earth’s mantle; so these lavas have inherited this rubidium-strontium composition from their mantle source.

However, what ages do these same methods yield when applied to rocks for whose formation there are independent cross-checks? There are up to 160 volcanic cones on the plateau to the north of the Canyon rim out of which these basalt lavas flowed.

The eruptions were so recent, occurring after the Grand Canyon formed, that some of these basalt lava flows cascaded like molten waterfalls over the Canyon rim, down the Canyon walls and into the Canyon, where they formed dams that temporarily blocked the flow of the Colorado River .

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The position of the Cardenas Basalt lava flows in the overall succession of rock layers in Grand Canyon can be seen in the generalized geologic “block” diagram of Grand Canyon .This radioactive decay is like the ticking of a clock, except instead of seconds these radioactive-decay “clocks” are said to measure in millions of years.By analyzing these parent and daughter elements in a rock and applying today’s measured rates of radioactive decay, geologists confidently claim they can calculate how long it took the radioactive decay of the parents to produce the measured quantities of daughters.In any case, could it be that these radioactive clocks have previously ticked at faster rates than they do today?There is much convincing evidence to support this possibility (see Further Reading at end of article).

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