AOAs appearance

The only cultivated AOA, Nitrospumilus maritimus, depends on CO2 as its only carbon source and the presence of even low levels of organic carbon were inhibitory to growth. The pathway of CO2 fixation is, however, unknown. Hyperthermophilic Crenarchaeota generally utilize a 3-hydroxypropionate pathway or a reductive TCA cycle for autotrophic carbon fixation. Another cultivated marine Crenarchaeota strain, Cenarchaeum symbiosum, a sponge symbiont, appears to use the 3-hydroxypropionate pathway. It cannot be concluded on this basis which pathway is used by the AOA, but it very likely that is not the Calvin cycle. N. maritimus had a minimal generation time of 21 h, longer but roughly on the same scale as AOB. 

Chondrites consist of four major components chondrules, FeNi-metal, refractory inclusions (Ca-Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)), and fine-grained matrix material. It is generally accepted that the refractory inclusions, chondrules, and FeNi-metal are formed in the solar nebula by high-temperature processes that included condensation and evaporation. Many CAIs and most chondrules and FeNi-metal were subsequently melted during multiple brief heating episodes. Matrix, some CAIs, and metal in some chondrites (e.g., CH and CB) appear to have escaped these high-temperature nebular... 

Although AOAs show no clear evidence of being melted, some appear to contain CAIs that have been melted (Figure 10). AOAs in CO3.0 chondrites contain 8 vol.% metallic Fe,Ni troilite is rare or absent (Chizmadia et al, 2002). 

A The relationship between chondrules, CAIs, and AOAs The contrasting mineralogy of CAIs and chondrules indicates that they formed at different nebular temperatures and perhaps in different nebular environments. This is confirmed by oxygen isotope studies which show that there are significant oxygen isotope compositional differences between chondrules and refractory CIAs and AOAs. Chondrules from C and O chondrites also have different oxygen isotope compositions and appear to have formed in different nebular environments. In contrast, CAIs from all chondrite types and AOAs are isotopically similar and share the... 

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