Results from different techniques, often measured in rival labs, continually confirm each other.Every few years, new geologic time scales are published, providing the latest dates for major time lines.
Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.In the past 150 years they have not found any fossils that Darwin would not have expected.The methods are all based on radioactive decay: The first radiometric dates, generated about 1920, showed that the Earth was hundreds of millions, or billions, of years old.Since then, geologists have made many tens of thousands of radiometric age determinations, and they have refined the earlier estimates.
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Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.