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For example, it has been known since the 1960s that the famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65 million years old.
Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. With modern, extremely precise, methods, error bars are often only 1% or so.
Every few years, new geologic time scales are published, providing the latest dates for major time lines.
Older dates may change by a few million years up and down, but younger dates are stable.
Paleontologists now apply sophisticated mathematical techniques to assess the relative quality of particular fossil successions, as well as the entire fossil record.
These demonstrate that, of course, we do not know everything (and clearly never will), but we know enough.
Current understanding of the history of life is probably close to the truth because it is based on repeated and careful testing and consideration of data.The geologic time scale was initially developed by determining the relative ages of rock units, first in Europe, and then in other parts of the world. To determine which rock units were older and which ones were younger (in a relative sense), geologists devised a number of laws, or principles, to help figure out the sequence of geologic events in a particular locality.In this lab, you will apply many of these laws and principles to determine the relative sequence of geologic events that created a particular set of rock layers and intrusions.In the past 150 years they have not found any fossils that Darwin would not have expected.New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of the great ‘tree of life’.
The discovery of means for absolute dating in the early 1900s was a huge advance.