How old is the Solar System? That is a question that cuts to the heart of it all. By studying several things, mostly meteorites, and using radioactive dating techniques, specifically looking at daughter isotopes, scientists have determined that the Solar System is 4.6 billion years old. Well, give or take a few million years. That age can be extended to most of the objects and material in the Solar System.
The United States Geological Survey(USGS) website has a lot of indepth material about how the age of the Solar System was determined. The basics of it are that all material radioactively decays into a stable isotope. Some elements decay within nanoseconds while others have projected half-lives of over 100 billion years. The USGS based their study on minerals that naturally occur in rocks and have half-lives of 700 million to 100 billion years. These dating techniques, known as radiometric dating, are firmly grounded in physics and are used to measure the last time that the rock being dated was either melted or disturbed sufficiently to re-homogenize its radioactive elements. This techniques returned an approximate age for meteorites of 4.6 billion years and Earth bound rocks around 4.3 billion years. The USGS admits that they were unable to find any rock that had not been altered by the Earths tectonic plates, so the age of the Earth could be refined in the future.
When the gasses of the early solar nebula began to cool, the first materials to condense into solid particles were rich in calcium and aluminum. Eventually solid particles of different elements clumped together to form the common building blocks of comets, asteroids, and planets. Astronomers have long thought that some of the Solar System’s oldest asteroids should be more enriched in calcium and aluminum, but, none had been identified until recently. The the Allende meteorite of 1969 was the first to show inclusions that were extremely rich in calcium and aluminum. It took 40 years for the spectra of the inclusions to be discovered and then extrapolates to very old asteroids still in orbit around the Sun. Astronomer Jessica Sunshine and colleagues made this discovery with the support of NASA and the National Science Foundation
Additionally, the Universe is thought to have been created about 13.7 billion years ago. Measuring two long-lived radioactive elements in meteorites, uranium-238 and thorium-232, has placed the age of the Milky Way at in the same time frame. From these measurements, it appears that large scale structures like galaxies formed relatively quickly after the Big Bang.
Here’s an article from Universe Today that gives more information about the radioactive dating process of studying meteorites, and another article about how the solar nebula probably lasted about 2 million years.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.