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Holmes saw tremendous potential in Boltwood’s technique, as well as room for improvement.

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Using the most up-to-date decay rates for uranium and radium, an intermediate decay product of uranium on the way to lead, he established an age of 370 million years for the syenites.He also recalculated Boltwood’s dates, adjusting each of the American’s figures by as much as 100 million years. 2002,” the young Holmes “realized there was no point in simply having an age for its own sake.When, in 1910, a 20-year-old student named Arthur Holmes signed on to work in his lab, now at London’s Imperial College, Strutt asked Holmes to pursue a more reliable method for determining radiometric ages.Holmes arrived at Imperial College on scholarship in 1907 and spent two years as a physics student, followed by a year in geology.Although each of these approaches offered vast improvements in dating, and collectively represented a fundamental sea change in the scientific understanding of the world, each had its flaws.

It would take the discovery of a demonstrably predictable phenomenon, radioactivity, to really expose the scope of Earth’s history.But the geologic timescale wasn’t always so settled.Prior to last century, estimates of Earth’s age — which of course constrained the ages of the various geologic periods recognized at the time — ranged broadly from thousands of years to more than 1 billion years.Silurian-aged rocks, named for an ancient tribe of Welsh Celts, contained abundant fossils of jawless fish as well as early coral fossils.Devonian-aged rocks, named for the English county of Devon, contained skeletons of jawed fish and the first terrestrial tetrapods and were typically found above Silurian rocks in the stratigraphic column.Ask how old Earth is and the answer will almost invariably be 4.55 billion years, give or take a few tens of millions of years.