3. Solar System Formation and Early Evolution: the First 100 Million Years

The solar system, as we know it today, is about 4.5 billion years old. It is widely believed that it was essentially completed 100 million years after the formation of the Sun, which itself took less than 1 million years, although the exact chronology remains highly uncertain. For instance: which, of the giant planets or the terrestrial planets, formed first, and how? How did they acquire their mass? What was the early evolution of the “primitive solar nebula” (solar nebula for short)? What is its relation with the circumstellar disks that are ubiquitous around young low-mass stars today? Is it possible to define a “time zero” (t ₀), the epoch of the formation of the solar system? Is the solar system exceptional or common? This astronomical chapter focuses on the early stages, which determine in large part the subsequent evolution of the proto-solar system. This evolution is logarithmic, being very fast initially, then gradually slowing down. The chapter is thus divided in three parts: (1) The first million years: the stellar era. The dominant phase is the formation of the Sun in a stellar cluster, via accretion of material from a circumstellar disk, itself fed by a progressively vanishing circumstellar envelope. (2) The first 10 million years: the disk era. The dominant phase is the evolution and progressive disappearance of circumstellar disks around evolved young stars; planets will start to form at this stage. Important constraints on the solar nebula and on planet formation are drawn from the most primitive objects in the solar system, i.e., meteorites. (3) The first 100 million years: the “telluric” era. This phase is dominated by terrestrial (rocky) planet formation and differentiation, and the appearance of oceans and atmospheres.     

Early Norian flora from Partizansk River Basin of Primorye, Russia

IntroductionThe Late Triassic strata andflora developed andwell outcropped in southern Pri morye,Russia.Thestrata are marine and non-marine alternate for eachother and yield abundant mollusk and plant fossilsinwhich the Late Triassic Mongugai flora is well-known in the world.Kryshtofovich(1910,1921,1924)and Kryshtofovich&Prynada(1932)studiedthis florainthe earlier ti me,and consequently,Sre-brodolyskaja(1958,1961,1968),Schorokhova(1975,1977,1997,2004)and Krassilov&Schorokhova(1970,1975)ma…     

Metal Dispersal and the Number of Population III Stars

Two fundamental constraints on the earliest star formation conditions in the Galaxy are an apparent empirical low-metallicity threshold of-4 ? [Fe/H], an and upper limit to the fraction of Population III halo stars of F _III < 4 × 10^-4. How do these observed constraints compare with predictions of simple models? This is investigated within the framework of element dispersal from clustered core-collapse SNe. Simple arguments considering turbulent mixing within multi-phase ISM suggest that the observed low-metallicity threshold is consistent with rough expected values. However, the observed limit on F _III is two orders of magnitude larger than predictions from this simple, one-zone inhomogeneous chemical evolution.     

The recognition of glacial retreat from palynological data: A review of recent work in the British Isles

Recent publications have presented palynological data from the early postglacial period in the British Isles, which have been interpreted as reflecting sequential glacial retreat following the Loch Lomond Stadial, The methodologies and results of these studies were examined and were concluded to be insufficient to demonstrate glacial retreat. A more cautious methodology was adopted and tested at several pollen sites in the Awe valley, Scotland. The results differed from previous studies in not demonstrating the sequence of palynological changes predicted from the hypothesis. These results need to be replicated at other localities, however, before the deglacial chronology hypothesis can be dismissed. Proposals to test the hypothesis further are suggested.     

Diagenetic signatures of stratal surfaces in the Upper Jurassic Fulmar Formation, Central North Sea, UKCS

Sedimentation rate and changes in relative sea level affect early diagenetic cementation along key stratal surfaces within the deeply buried Upper Jurassic Fulmar Formation, South Central Graben, UKCS. As a result of the bioturbated nature of the shallow marine strata, variations in ichnofabrics and cross-cutting relationships between trace fossils are important in identifying and correlating stratal surfaces. Two transgressive and two regressive surfaces/sequence boundaries were studied, using petrographical, mineralogical and geochemical techniques. Cements, including early diagenetic pyrite framboids, grain-rimming apatite, microcrystalline dolomite and ankerite, occur at, above and immediately below both transgressive and forced regressive surfaces/sequence boundaries. Breaks or subdued rates of sedimentation associated with both types of surfaces meant that the sediment package resided within early diagenetic zones for prolonged periods of time, enhancing diagenetic reactions at and below the surfaces. The distribution of ankerite, despite being a deep-burial cement, was primarily controlled by concentrations of bioclasts that are particularly abundant at transgressive surfaces. The diagenetic character of the forced regressive surfaces/sequence boundaries is more complex than that of the transgressive surfaces, both in terms of mineralogy and paragenesis. This is attributed to the superimposition of diagenetic assemblages as a result of erosion, re-sedimentation and sediment by-passing. Although the diagenetic signature of the surfaces has been modified by dissolution/replacement reactions during deep burial, early diagenetic signatures can still be distinguished.     

Geochemical discriminations of sandstones from the Mohe Foreland basin,northeastern China: Tectonic setting and provenance

The Mohe region near the border area of China with Russia is in Heilongjiang Province. Topographically the area consists of lower mountains or hills situated at the northern end of the Da Hinggan Mountains. Struc-turally the Mohe basin rests on the north margin of the Ergun Block, and the Mongol-Okhotsk Orogen is lo-cated to the north of the basin. Due to poor access conditions and good vegetation coverage, previous researches on the basin are much weak with few spe-cial geological inves…