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Ordinary rocks, for example, may be millions or billions of years old, and are free for the taking.
But rocks you're likely find along a nature trail or highway are mere infants compared to the oldest rocks on Earth.
Moon rock samples collected during the Apollo missions have been dated to about 4.5 billion years, besting our oldest terrestrial rocks by a few hundred million years. Email it to Life's Little Mysteries and we'll try to answer it.
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Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium-87 compared with the stable isotopes.
This relative abundance is expressed as the Sr ratio, where strontium-86 is chosen to represent the stable isotopes strontium-88, strontium-86, and strontium-84, which occur in constant proportions in natural materials.
Sedimentary rocks, such as sandstone, are created by the compression of sediment or particles.
Using estimates of measurement precision, the crucial question of whether or not scatter outside of measurement error exists is addressed.
Dissolved strontium in the oceans today has a value of 0.709 that is dependent on the relative input from the continents and the ridges.
In the geologic past, changes in the activity of these two sources produced varying Sr ratios over time.
In contrast, Earth’s most abundant lava rocks, which represent the mantle and make up the major oceanic ridges, have values between 0.703 and 0.705.
This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70,000, it is quite significant.