Geochemical and mineralogical study for estimating past oxygen partial pressure from ancient cosmic spherules

宇宙小球体是直径小于1毫米的亚球形或球形颗粒，是由星际尘埃和大型物体在进入大气层时熔化产生的。虽然人们主要从极地冰盖和新生代深海沉积物中发现宇宙球粒，但也从远洋石灰岩和放射虫燧石沉积岩中发现了一些比中生代更古老的宇宙球粒。这些沉积岩中的宇宙球含有大气中的氧，它们最终的氧化状态由过去大气中的氧含量决定。对沉积岩中古代宇宙小球体的系统研究可以探测到过去大气中氧分压的长期变化。

Cosmic spherules are subspherical to spherical particles of <1 mm diameter which are produced by melting of interplanetary dust and large objects during atmospheric entry. Although cosmic spherules are known principally from the ice sheets of polar regions and Cenozoic deep-sea sediments, a few spherules older than Mesozoic were recovered from the sedimentary rocks of pelagic limestone and radiolarian chert. The cosmic spheres from these sedimentary rocks contain atmospheric oxygen, and their final oxidation state is determined by the past oxygen content of the atmosphere. Systematic studies of ancient cosmic spherules in the sedimentary rocks could detect long-term changes in the past oxygen partial pressure of the atmosphere.