Age of the Solar System Evidence of Solar System Origins from Radiometric Dating

Radiometric dating uses the radioactive decay of heavy elements to tell time PA STEM Science Radioactive decay is mostly independent of external influences Decay times span a large range: billions of yrs Heavy elements are found in a wide range of materials

Radioactive decay is a natural result of dynamic interactions in large nuclei PA STEM Science Protons in the nucleus strongly repel each other Protons and neutrons in the nucleus attract each other by the strong nuclear force Stability of the nucleus is determined by the interplay between these two effects

Larger nuclei require more neutrons to counteract proton repulsion PA STEM Science Protons in the nucleus strongly repel each other Protons and neutrons in the nucleus attract each other by the strong nuclear force Stability of the nucleus is determined by the interplay between these two effects

Larger nuclei require more neutrons to counteract proton repulsion PA STEM Science

Uranium isotopes are good examples of long-lived nuclei, decaying over billions of years PA STEM Science

There are two main ways that heavy nuclei decay PA STEM Science Alpha decay nucleus gives off a 4 He nucleus (2 protons, 2 neutrons) Beta decay neutron changes to proton and gives off an electron n → p + e -

Heavy elements continue alpha and beta decay until a stable nucleus is reached PA STEM Science

Time of decay is measured by the half-life, which is the time for half the radioactive nuclei to change into stable nuclei PA STEM Science # of half-lives parent daughter 1 1/2 1/2 2 1/4 3/4 3 1/8 7/8 4 1/16 15/16

A number of radioactive nuclei have half- lives of use in dating the solar system PA STEM Science Parent Half-life (years) Daughter 87 Rb billion 87 Sr Th billion 208 Pb U billion 206 Pb K billion 40 Ar U billion 207 Pb 82

Solar system should be the same age as the oldest meteorites (4.567 billion years) PA STEM Science

Both CAIs and chondrules in meteorites can be dated to this earliest period PA STEM Science The average age of the earliest material is ± billion years 1 1. James N. Connelly, et al., Science 338, 651 (2012)

CAIs formed quickly but chondrules continued forming for 3 million years PA STEM Science The CAIs may have formed within 50,000 years of the start of the solar system 1 1. James N. Connelly, et al., Science 338, 651 (2012)

Inferred relative abundances of short-lived isotopes 182 Hf and 129 I reveal the pre- history of the solar system PA STEM Science 1. Maria Lugaro, et al., Science 345, 650 (2014)

Earth must be younger than the solar system but older than the oldest rocks PA STEM Science The famous Jack Hills zircons (Australia) are dated to billion years ago

Other surface rocks support this dating PA STEM Science Ages of rocks from Mars and the Moon also support it