“In Earth sciences there’s a need to be able to define what happened first and what happened second.” Geochemists age rocks by measuring the ratio of radioactive isotopes – versions of the same element with different atomic masses – in them.Because the elements decay from one isotope, or element, to another at a constant rate, knowing the ratio in a particular rock gives its age.
One of the favourites for tracing events in the early solar system, such as when the Earth’s crust differentiated from its mantle or when the lava oceans on the moon solidified, is samarium-146, a hard shiny metal found in many minerals in the Earth’s crust.
“In this time window, there are not many other chronometers,” says Michael Paul of the Hebrew University in Jerusalem.
The discovery gave scientists a tool for dating rocks that contain radioactive elements.
Many elements have naturally occurring isotopes, varieties of the element that have different numbers of neutrons in the nucleus.
Both elements are used by geologists to date rocks and chart the history of events on our planet and in the solar system.
“If you have a critical event in Earth’s history, something like an extinction event or a climate change shift or a meteorite impact, you need to know the absolute age with the most confidence,” says Joe Hiess of the British Geological Survey, who led one of the studies.How radiometric dating works in general Why methods in general are inaccurate Why K-Ar dating is inaccurate The branching ratio problem How Errors Can Account for the Observed Dates Why older dates would be found lower in the geologic column especially for K-Ar dating Do different methods agree with each other on the geologic column?Possible other sources of correlation Anomalies of radiometric dating Why a low anomaly percentage is meaningless The biostrategraphic limits issue Preponderance of K-Ar dating Excuses for anomalies Need for a double-blind test Possible changes in the decay rate Isochrons Atlantic sea floor dating Dating Meteorites Conclusion Gentry's radiohaloes in coalified wood Carbon 14 dating Tree ring chronologies Coral dating Varves Growth of coral reefs Evidence for catastrophe in the geologic column Rates of erosion Reliability of creationist sources Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium.Different elements and isotopes decay at vastly different rates.Scientists pick one that suits the timescale of interest.Since there doesn't seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.