![]() ![]() "They are critical witnesses to the processes that were happening while the solar system was forming," says Tissot. This inclusion contains strontium, which was isolated and studied by Tissot and colleagues. As such, CAls offer a geologic window into how and from what type of stellar materials the solar system formed.Ī CAI inclusion in the Allende meteorite. ![]() Dating back 4.567 billion years, CAIs represent the first objects that condensed in the early solar nebula, the flattened, rotating disk of gas and dust from which the solar system was born. CAIs are calcium- and aluminum-rich inclusions found in certain meteorites. In the latter scenario, i.e., with less rubidium, the newly formed Earth would have been poor in volatiles such as water, thus the amount of Sr-87 in the earth and in volatile-poor meteorites would be similar to that observed in the oldest-known solar system solids, the so-called CAIs. In theory, the Rb–Sr chronometer should be able to tease apart these two scenarios, as the amount of Sr-87 produced by radioactive decay in a given amount of time will not be the same if Earth started with a lot of rubidium versus less of the material. Understanding which of these scenarios took place is important for understanding the origin of water on Earth. As such, rubidium is present at a higher proportion in solar system objects that are rich in other volatiles (such as water), because they formed at lower temperatures.Ĭounterintuitively, Earth has an Rb/Sr ratio that is 10 times lower than that of water-rich meteorites, implying that the planet either accreted from water-poor (and thus rubidium-poor) materials or it accreted from water-rich materials but lost most of its water over time as well as its rubidium. What is particularly attractive about using the Rb–Sr pair for dating is that rubidium is a volatile element-that is, it tends to evaporate to form a gas phase at even relatively low temperatures-while strontium is not volatile. Rubidium-87, in contrast, can be used to date the oldest objects in the universe, and, closer to home, the objects in the solar system. ![]() The most famous radioactive isotope used for dating is carbon-14, the radioactive isotope of carbon with its half-life of roughly 5,700 years, carbon-14 can be used to determine the ages of organic (carbon-containing) materials on human timescales, up to about 60,000 years. Half-life represents the amount of time required for the radioactivity of an isotope to drop to one-half its original value, allowing these isotopes to serve as chronometers for dating samples on varying time scales. Rubidium-87 has a very long half-life, 49 billion years, which is more than three times the age of the universe. Scientists have found that strontium is useful when attempting to date objects from the early solar system because one of its heavy isotopes, strontium-87, is produced by the decay of the radioactive isotope rubidium-87 (atomic symbol: Rb). Strontium (atomic symbol: Sr), a chemically reactive metal, has four stable isotopes: strontium-84 and its heavier cousins that have 86, 87, or 88 neutrons in their nuclei. "We want to know what the nature of this material is and ho w it fits into the mix of ingredients that went to form the recipe for the planets." "This is really interesting," Charlier says. The discovery points to the likely existence in meteorites of nanometer-sized grains containing almost pure strontium-84 that were formed during a rare nucleosynthetic process before the formation of the solar system itself Charlier of Victoria University of Wellington are co-lead authors on a study describing the findings that was published in Science Advances on July 9. This is exciting, as the physical identification of such grains would provide a unique chance to learn more about the p-process." "Our results points to the survival of grains possibly containing pure strontium-84. Tissot, assistant professor of geochemistry. "Strontium-84 is part of a family of isotopes produced by a nucleosynthetic process, named the p-process, which remains mysterious," says Caltech's François L. Scientists have discovered a new type of star dust whose composition indicates that it formed during a rare form of nucleosynthesis (the process through which new atomic nuclei are created) and could shed new light on the history of water on Earth.Ī team led by cosmochemists from Caltech and Victoria University of Wellington in New Zealand studied ancient minerals aggregates within the Allende meteorite (which fell to Earth in 1969) and found that many of them had unusually high amounts of strontium-84, a relatively rare light isotope of the element strontium that is so-named for the 84 neutrons in its nucleus. ![]()
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