Planetesimals were already forming by ∼1 Myr after CAI formation, consistent with their growth predominantly through the accretion of chondrules.Nebular chondrule formation was completed by ∼5 Myr after CAI formation when the impact-generated Cba chondrules formed after the disk was cleared of gas and dust.
Until a cross-calibration exercise using synthetic and natural standards establishes the reproducibility between laboratories, only ages from a single laboratory, or between laboratories having demonstrated concordance, can provide a reliable relative chronometric framework for the formation and evolution of the early Solar System.
Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
We recognize that there is some debate over the age of the Solar System, but conclude that an age of 4567.30 ± 0.16 Ma based on four CAIs dated individually by the same method in two different laboratories is presently the best constrained published value.
We further conclude that nebular chondrules dated by the Pb–Pb method require that they formed contemporaneously with CAIs and continued to form for at least ∼4 Myr, a conclusion that implies heterogeneous distribution of the short-lived Al nuclide in the protoplanetary disk.
Sometimes, however, numerous discordant dates from the same rock will plot along a line representing a chord on the Concordia diagram. is then interpreted to be the date that the system became closed, and the younger date, t*, the age of an event (such as metamorphism) that was responsible for Pb leakage.
Pb leakage is the most likely cause of discordant dates, since Pb will be occupying a site in the crystal that has suffered radiation damage as a result of U decay.Such trapped Ar is not problematical when the age of the rock is in hundreds of millions of years.The dating equation used for K-Ar is: Carbon Dating Radiocarbon dating is different than the other methods of dating because it cannot be used to directly date rocks, but can only be used to date organic material produced by once living organisms.But, again, exptrapolation of the discordia back to the two points where it intersects the Concordia, would give two ages - t* representing the possible metamorphic event and t and solve for t . This argument tells when the elements were formed that make up the Earth, but does not really give us the age of the Earth. Thus, our best estimate of the age of the Earth is 4.55 billion years.Nd ratios on several minerals with a mass spectrometer and then from the slope determine the age of the rock. If a magma cools quickly on the surface of the Earth, some of the Ar may be trapped.Pb, respectively, have appropriate half-lives to resolve the ages of meteorites and their components formed in the first 5 Myr of the Solar System.