Solar System early history

The cratered surfaces of asteroids and terrestrial planets underscore the importance of impacts for the formation and evolution of the solar system. Early in the history of the solar system such collisions were the mechanism for accretion of planetesimals and finally the planets themselves [1], The effects of these still ongoing collisions are visible from the megascopic down to the submicroscopic length scale, i.e., they range from large impact craters and their ejecta blankets down to shock-metamorphic effects in minerals [2-4]. These effects form as a result of the interaction of strong shock waves with the affected solid matter. 

Most meteorites are chondrites, so-called because almost all contain spherical mm- to cm-sized chondrules or their fragments early in the Solar System s history. Cooling rates for some were 1000 C/hr, and 10-100°C/hr for others. Rapid heating and cooling are easily done in the laboratory but difficult on a Solar System scale. Yet, large volumes of chondrules must have existed in the Solar System because chondrites are numerous (Table I). Chondrites (and many achondrites) date to the Solar System s formation - indeed provide chronometers for it and represent accumulated primary nebular condensate and accretionary products. Some condensate formed from the hot nebula as mm-sized Ca- and Al-rich inclusions (CAI), mineral aggregates predicted as vapor-deposition products by thermodynamic calculations. These CAI, found mainly in chondrites rich in carbonaceous (organic) material exhibit many... 

Grossman, L. Larimer, J. W. (1974). Early chemical history of the solar system. Rev. Geophys. Space Phys., 12, 71-101. 

Fahey AJ, Goswami JN, McKeegan KD, Zinner EK (1987) Al, Pu, Ti, REE, and trace element abundances in hibonite grains from CM and CV meteorites. Geochim Cosmochim Acta 51 329-350 Fowler WA, Greenstein JL, Hoyle F (1962) Nucleosynthesis during the early history of the solar system. Geophys J 6 148-220... 

Rolfs CE, Rodney WS (1988) Cauldrons in the cosmos. University of Chicago Press, Chicago Rotaru M, Birck JL, Allegre CJ (1992) Clues to early solar system history from chromium isotopes in carbonaceous chondrites. Nature 358 465-470... 

Wasson JT (1985) Meteorites Their Record of Early Solar System History. New York Ereeman Wesolowski DJ, Benezeth P, Palmer DA (1998) ZnO solubility and Zrf+ complexation by chloride and sulfate in acidic solutions to 290°C with in-situ pH measurement. Geochim Cosmochim Acta 62 971-984 Wessel P, Smith WHF (1991) Free software helps map and display data. EOS Trans AGU 72 445-446 Xiao Z, Gammons CH, Williams-Jones AE (1998) Experimental study of copper(I) chloride complexing in hydrothermal solutions at 40 to 300°C and saturated water vapor pressure. Geochim Cosmochim Acta 62 2949-2964... 

Solution Because the Initial Al/ Al ratio in meteorite 1 is greater, meteorite 1 formed earlier. That is, meteorite 1 has an older age. Because the initial ratio in meteorite 2 is half of that in meteorite 1, the age difference is the half-life, which is 0.71 million years. That is, meteorite 1 is older than meteorite 2 by 0.71 Ma. If the age of meteorite 1 is 4562 Ma, then the age of meteorite 2 is 4561.3 Ma. This example shows that using extinct nuclides can distinguish small age differences in the early evolution history of the solar system. 

This isotope is particularly significant, as it is thought to have been a potent source of heating for asteroids and planets early in solar system history. A variety of other shortlived isotopes have now been confirmed in meteorites and are the basis for high-resolution chronometry of the early solar system. 

If an internal isochron cannot be generated, a model age can be determined from the measured 207pb /206Pb of the sample and the assumed initial lead isotopic ratios. For studies of the early solar system, this initial lead composition is assumed to be that measured in troilite (FeS) from the Canyon Diablo meteorite. Troilite is a uranium-free mineral and its host meteorite formed very early in the history of the solar system. Because the U/Pb ratio of the solar system is low, the lead incorporated into the troilite should not have evolved significantly from the initial composition in the solar system. 

One drawback of the Pb-Pb system is that two-stage or three-stage evolution of the U-Pb isotopic system can produce linear arrays on a Pb-Pb isochron plot (Gale and Mussett, 1973). If these arrays are interpreted as single-stage isochrons, incorrect dates may be obtained. In some cases, measurements of the U/Pb ratio can help identify multistage samples. But if several events occurred sufficiently early in solar system history, even a concordia approach may not be able to identify a multistage system (Tera and Carlson,... 

Wasserburg, G. J. and Papanastassiou, D. A. (1982) Some short-lived nuclides in the early solar system a connection with the placental ISM. In Essays in Nuclear Astrophysics, eds. Barnes, C. A., Clayton, D.D. and Schramm, D.N. Cambridge Cambridge University Press, pp. 77-140. A good review of the early history of chronology using short-lived radionuclides. 

When were the atoms that became our solar system synthesized The star formation rate in the galaxy was highest early in galactic history and a lot of heavy elements were produced. However, most of this material was subsequently incorporated into stars, and much of that has been permanently sequestered. On the other hand, much of the recently synthesized material has not yet been incorporated into a new generation of stars. This balance between synthesis and sequestration means that the birth dates of the elements that became the solar system are roughly evenly distributed over the 7.5 Gyr of galactic history prior to the solar system s birth (Clayton, 1988). 

The tools that we have to determine the age of the solar system and the chronology of early solar system materials are the long-lived and short-lived radiochronometers discussed in Chapter 8. The long-lived radionuclides tell us that the oldest objects in the solar system formed at -4.5-4.6 Ga (Fig. 9.8). But the precision of most of these measurements is not sufficient to investigate the details of those early times. In addition, there are uncertainties in the half-lives of the different radionuclides that translate into absolute uncertainties of several million to tens of millions of years. Short-lived radionuclides provide the time resolution necessary to unravel the details of early solar system history. 

In addition to the possible extended formation history of some CAIs, many CAIs show clear evidence of later heating events, probably in the parent body, that disturbed or reset the Al-Mg systematics. These reset inclusions make up the peak at around zero in the 26A I/27 AI histogram shown in Figure 8.26. These disturbed inclusions complicate the interpretation of the isotopic record of the early solar system. 

These anomalies are interpreted as being caused by the decay of 129I and 244Pu in the early history of the solar system (9, 15, 18). 

Wasson, J. T. Meteorites. Their Record of Early Solar-System History, W. H. Freeman and Company, New York 1985... 

The W isotopic compositions of various terrestrial samples, chondrites, iron meteorites, basaltic achondrites, lunar samples, and Martian meteorites are expressed as deviations in parts per 104 from the value for the silicate earth (such as the W in a drill bit or chisel), which are the same as those of average solar system materials, represented by carbonaceous chondrites. These values are summarized in Fig. 8.9, from which it can be seen that early segregated metals such as the iron meteorites and metals from ordinary chondrites have only unradiogenic W because they formed early with low Hf/W. The time differences between metal objects segregated from parents with chondritic Hf/W are revealed by the differences in W isotopic compositions between each of the metal objects and chondrites. The Hf-W model ages of all these metals indicate that all of their parent bodies formed within a few million years, implying rapid accretion in the early history of the solar system. 

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