Transient heating events that formed calcium-aluminum–rich inclusions (CAIs) and chondrules are fundamental processes in the evolution of the solar protoplanetary disk, but their chronology is not understood. Using U-corrected Pb-Pb dating, we determined absolute ages of individual CAIs and chondrules from primitive meteorites. CAIs define a brief formation interval corresponding to an age of 4567.30 ± 0.16 million years (My), whereas chondrule ages range from 4567.32 ± 0.42 to 4564.71 ± 0.30 My. These data refute the long-held view of an age gap between CAIs and chondrules and, instead, indicate that chondrule formation started contemporaneously with CAIs and lasted ~3 My. This time scale is similar to disk lifetimes inferred from astronomical observations, suggesting that the formation of CAIs and chondrules reflects a process intrinsically linked to the secular evolution of accretionary disks.

https://science.sciencemag.org/content/sci/338/6107/651.full.pdf

The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk

Application of Fe isotopes to tracing the geochemical and biological cycling of Fe

As with all science, our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data. This process invigorates the intellectual foundation on which old models are tested and new concepts are built. Just as the application of new observational tools to lunar science in 1610 (Galileo’s telescope) and 1840 (photography) yielded breakthroughs concerning the true nature of the lunar surface, the computational and technological advances highlighted by the Apollo and post-Apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the Moon.

### 1.1. Pre-Apollo view of the thermal and magmatic evolution of the Moon

Many of the early views of the Moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the Sun and the Moon. Prophetically, myths involving the lunar deities Mwuetsi from Zimbabwe and Coyolxauhqui from Mexico told of rather violent or catastrophic events in which the Moon was expunged from the Earth. Numerous ancient scientific observations were made about the nature of the Moon ranging from those uncovered in early Neolithic sites that correctly identified mare Crisium and mare Humorum to the insights made by Greek philosophers such as Anaxagoras (ca. 500-428 B.C.) and Democritus (ca. 460-370 B.C.), who attached terrestrial analogues to its character (stone, mountains).

With the advent of the telescope (1610) and photography (1840) as scientific tools for lunar exploration, semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation. Initially, modern terrestrial geological analogs were extended to the Moon (lunar highlands, volcanic craters, seas). Combined with the rigors of computational modeling, these observational data were extended to predict the original thermal state of the Moon and its thermal and magmatic history. Its proximity to the Earth …

Thermal and Magmatic Evolution of the Moon

Major advances in deciphering the record of nebula processes in chondrites can be attributed to analytical improvements that allow coordinated isotopic and mineralogical studies of components in chondrites and to a wealth of new meteorites from hot and cold deserts. These studies have identified a few rare pristine chondrites that largely escaped heating and alteration in asteroids, which have matrices composed of submicrometer-sized grains of enstatite and forsterite and amorphous silicates, as found in comets. Isotopic analyses of components in pristine chondrites using short-lived nuclide chronometers, Pb-Pb dating, and oxygen isotopes aided by laboratory and theoretical studies of chondrites and differentiated meteorites have provided key constraints on the processes that shaped the early solar system. These processes were once thought to have followed one another sequentially over a period of several million years: chondrule formation; planetesimal accretion; alteration, metamorphism, and mel...

http://www.higp.hawaii.edu/~escott/Annual%20Rev%20chond.pdf

Chondrules and the Protoplanetary Disk

Magnesium isotopic composition of the Earth and chondrites

http://geosci.uchicago.edu/~fciesla/Chronology/2009/krot_etal_2009.pdf

Origin and chronology of chondritic components: A review

The high time resolution Pb-Pb ages and short-lived nuclide based relative ages for CAIs and chondrules are reviewed. The solar system started at 4567.2 {+-} 0.6Ma inferred from the high precision Pb-Pb ages of CAIs. Time scales of CAIs ({le}0.1Myr), chondrules (1-3Myr), and early asteroidal differentiation ({ge}3Myr) inferred from {sup 26}Al relative ages are comparable to the time scale estimated from astronomical observations of young star; proto star, classical T Tauri star and week-lined T Tauri star, respectively. Pb-Pb ages of chondrules also indicate chondrule formation occur within 1-3 Myr after CAIs. Mn-Cr isochron ages of chondrules are similar to or within 2 Myr after CAI formation. Chondrules from different classes of chondrites show the same range of {sup 26}Al ages in spite of their different oxygen isotopes, indicating that chondrule formed in the localized environment. The {sup 26}Al ages of chondrules in each chondrite class show a hint of correlation with their chemical compositions, which implies the process of elemental fractionation during chondrule formation events.

/pdf/constraints-on-the-origin-of-chondrules-and-cais-from-short-3k9iul7saa.pdf

Constraints on the Origin of Chondrules and CAIs from Short-lived and Long-Lived Radionuclides

/pdf/constraints-on-the-origin-of-chondrules-and-cais-from-short-4uzcbi1z3p.pdf

Constraints on the Origin of Chondrules and CAIs from Short-Lived and Long-Lived Radionuclides

Concordant Rb–Sr, Sm–Nd, and Ar–Ar ages for Northwest Africa 1460: A 346 Ma old basaltic shergottite related to “lherzolitic” shergottites

Isotopic and elemental composition of iron, nickel, and chromium in type I deep-sea spherules: implications for origin and composition of the parent micrometeoroids

L. E. Nyquist

Papers

Origin and chronology of chondritic components: A review

Constraints on the Origin of Chondrules and CAIs from Short-lived and Long-Lived Radionuclides

Constraints on the Origin of Chondrules and CAIs from Short-Lived and Long-Lived Radionuclides

Concordant Rb–Sr, Sm–Nd, and Ar–Ar ages for Northwest Africa 1460: A 346 Ma old basaltic shergottite related to “lherzolitic” shergottites

Isotopic and elemental composition of iron, nickel, and chromium in type I deep-sea spherules: implications for origin and composition of the parent micrometeoroids