Isotope best dating very old rocks
Biologists actually have at their disposal several independent ways of looking at the history of life - not only from the order of fossils in the rocks, but also through phylogenetic trees. Relative dating is done by observing fossils, as described above, and recording which fossil is younger, which is older.The discovery of means for absolute dating in the early 1900s was a huge advance.
Today, innovative techniques provide further confirmation and understanding of the history of life.
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.
"We've proved that the chemical record inside these zircons is trustworthy," said John Valley, lead study author and a geochemist at the University of Wisconsin, Madison. Trace elements in the oldest zircons from Australia's Jack Hills range suggest they came from water-rich, granite-like rocks such as granodiorite or tonalite, other studies have reported.
That means Earth cooled quickly enough for surface water and continental-type rocks just 100 million years after the moon impact, the massive collision that formed the Earth-moon system. ] "The zircons show us the earliest Earth was more like the Earth we know today," Valley said.
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