Reading: MacPherson et al. (2005)
1. Create a list of phrases that describe the most important properties of CAIs. Include the following: chemistry; mineralogy; shapes and textures; occurrence.
2. What are FUN objects, and what aspect of their isotopic compositions do the authors consider to be most difficult to explain?
3. Briefly summarize the key evidence for believing that CAIS formed (a) in a restricted environment close to the protosun; (b) by volatility-controlled processes at high temperature; and (c) in a slowly-cooling environment.
4. According to the authors, what measurements or approaches need to be made to resolve the following: (a) the roles of condensation and distillation in establishing the bulk compositions of CAIs; (b) whether there are any age differences between CAI types and chondrules; (c) the genetic relationship between CAIs and chondrules; and (d) the origin of size and type sorting of CAIs and chondrules.
5. BONUS QUESTION (ANSWER IF YOU CAN): CAIs are often enriched in refractory elements (those with high 50% condensation temperatures; see Davis (2006) reading) relative to CI chondrite "cosmic abundances" by a factor of ~20x. Rare-earth-elements (REEs), which are used to classify CAIs, are good examples of such refractory elements. Thus, Fig. 3 shows a ~20x enrichment in REE for the 'unfractionated' pattern. Conversely, volatile elements (those with low 50% condensation temperatures) tend to be depleted in CAIs. If CAIs formed by condensation or distaillation in a system with overall cosmic composition, what is the significance of the factor 20x enrichment in refractory elements?