A Naprendszer geokémiája
• • • • •
Formation of Universe: 15 billion years Formation of Galaxy: 11 billion Years Formation of Solar System: 4.6 billion years Sun is probably a third generation star Probably takes 10-100 million years for planets to form
A Nap T-Tauri fázisa • Sun was initially hotter and bigger than it is now the superluminous phase lasted ~10 My and blew off ~25% of it’s mass • H and He were very abundant, but the solar wind resulting from this T-Tauri phase (TTauri star: TTS) blew most of it out of the solar system (Változó kistömegű csillag, elemfejlődés C-ig.)
Image credit: IAU
8 bolygó, 39 hold kb. 50 ezer aszteroida építi fel Nap m 740x
Our Solar System is Not Typical • Over 100 extrasolar planets (exoplanet) known • Barely can detect Jupiter-size planets, don't yet have technology to see small planets • Many have very eccentric orbits • Some have gas giants very close in to sun ("hot Jupiters")
Elemek gyakorisága a Naprendszerben Honnan tudjuk? - A Nap (és a többi csillag) spektroszkópos tanulmányozása, - A meteoritok (aszteroida öv, Mars, Hold, kondrit), továbbá földi, holdi és marsi kőzetek elemzése, - Fizika, kémia (elméleti, kisérleti) - Hogyan kondenzálódtak a teljes Naprendszer szilárd anyagai, a bolygók, és hogy szórtírozódtak az elemek a Naprendszerben?
Kondrit If the Sun and Solar System formed from the same material at the same time, we would expect the raw material of the planets to match the composition of the Sun, minus those elements that would remain as gases. A class of meteorites called chondrites shows such composition, which are thought to be the most primitive remaining solar system material. Chondrites are considered the raw material of the inner Solar System and reflect the bulk composition of the Earth. belső bolygók = Nap – gázok = kondrit
Normál kondrit (morzsalékos, összetapadt csomók aggregátuma, nincs mátrix), a csomók/cseppek több fázisból állnak.
Normál kondritban kondrumok.
A kondrit összetétele A kondrit összetétele
A Nap összetétele A Nap összetétele
The highly volatile elements H, C, N, O and noble gases are depleted in C1 meteorite relative to the Sun photosphere. Li is depleted in the Sun.
Zr
The Sun is basically H+He, whereas the Earth is dominated by O, Si, Mg, Fe, S, Al, Ca. Much Fe is in core, leaving rocky earth dominated by O, Si, Mg.
Elemek a Naprendszerben
Nap+C1 szenes kondrit
Faure, 1998
Kozmikus összetétel? • A Naprendszer (valójában a Nap) elemi összetétele kozmikus (csillag) elemi gyakoriság (Li, Be, B) • A Naprendszer (valójában a Nap) elemi összetétele gázok = szenes kondrit (Naprendszer ősi állapotát tükröző meteorit) Föld (és a többi belső bolygó is) kondritos összetételű (volt?)
Az anyag körforgása The cycle of matter between the interstellar clouds and stars leads to the evolution of the chemical composition of the Universe. Part of the material of this cycle falls and remains bound in black dwarf neutron stars and black holes.
In the Nebular Hypothesis, a cloud of gas and dust collapsed by gravity begins to spin faster because of angular momentum conservation. As the nebula collapses further, local regions begin to contract gravitationally on their own because of instabilities in the collapsing, rotating cloud condensation Protosun and Protoplanets
The collapsing, spinning nebula begins to flatten into a rotating pancake.
Heating occurred due to potential energy increase. Volatilization occurred in the central hotter regions, casting the volatiles into the outer regions. Only such elements as (Ca, Al, Th, U), Si, Mg, Fe, etc. (so-called more refractory elements) remained in the inner regions. H, C, N, O forming ice crystals (H2O, methane, CO2, ammonia, nitrogen) moved into the outer regions.
Formation of Planets • Planets formed by accretion of smaller objects = impact • Very tiny objects hold together by atomic forces • Objects kilometers across hold together by gravity • As planets get bigger, gravity gets stronger, impacts get more violent • Big impacts throw out ejecta, trap heat
A bolygókeletkezés folyamatának sematikus ábrája az időskálával A bolygók szilárd magjai porszemcsék összetapadásából keletkeznek a protoplanetáris korongban. 1/ a gáz és por részecskék szeparációja porszemcsék "leülepedése” gravitáció hatására a korong fősíkjában a részecske a fősík felé halad összetapad a környező porszemcsékkel, és így tovább. Min. 1 km méretű bolygócsírák között gravitációs vonzás lép fel ütközés összetapadás és/vagy aprózódás, azonban az ütközéskor keletkezett törmelék nem szökik meg, hanem visszahull a felszínre eredmény az ún. elszabadult növekedés. (a ~km átmérőjű populációból véges számú nagyméretű bolygókezdemény alkul ki). Az oligarchikus növekedés fázisában ezek további, kisebb testeket abszorbeálnak, amely folyamat végén kialakul kb. néhány száz protobolygó, amelyek mérete 103-104 km A földszerű bolygók lassan épülnek fel, további ~108 év alatt, kisebb tömegű protobolygók összetapadásával, amelyek úgy perturbálják egymás pályáját, hogy az végül nagy ütközési rátához vezet. A nagyobb tömegű protobolygók képesek arra, hogy magukhoz vonzzák a környezetükben található gázt. Ez az akkréció a szilárd magra nagyon gyors, és nagyon gyorsan véget is ér, mert a gáz elhasználásával a korongban az óriásbolygó körül egy rés keletkezik a gravitációs árapály erők miatt. A továbbiakban a bolygók - akár földtípusúak, akár óriásbolygók számottevően már nem növekednek tömegükben, a bolygókeletkezés befejeződött, bár az égitestek még néhányszor 108 évig folyamatos bombázásnak vannak kitéve a kisebb méretű testek, bolygókezdemények és üstökösmagok által, mint az a Naprendszer esetében jól ismert. ELTE, Csillagászati Tanszék
Refrakter (hő-/tűzálló, “makacs”) és volatil (illó) elemek (kozmokémiai /kondenzációs ill. illékonyságai/ sajátosság nagy T, kis p)
Refrakter elemek: nagy olvadáspontú, szilárd fázisban korai kondezáció a napködből a hűlés során (átmeneti refrakter) Volatil elemek: kis olvadáspontú, illó fázisban kis hőmérsékletű kondenzáció és szublimáció (a napködben nincs folyékony fázis a kis P miatt) (gyengén, erősen)
ammonia
Kondenzációs sorozat
Anderson, 2007
Fig. 35.8 During condensation of the solar nebula, the protoplanet earth formed by accretion and differentiation of components, largely on the basis of their different densities (after Ringwood, 1975). PTA, primitive terrestrial atmosphere.
Wenk Bulakh, 2013
Mineral evolution over earth’s history In Chapter 34 and earlier in this chapter, we have described the present-day mineral composition of the earth, the moon, and the planets. We also presented general models on how the first minerals may have formed in the solar system and subsequently accreted in planets. Looking closer to home, how have minerals evolved during the history of the earth? Much of the interpretation of the early history of mineral development on earth is based on characteristic isotope data of minerals found in various classes of meteorites, rocks from the moon, and terrestrial rocks. As we have seen, the hot solar nebula initially condensed into protoplanets, their satellites, and asteroids. Below 1500 K, in a turbulently convecting hydrogen silicate atmosphere, many minerals precipitate, including olivine, diopside, feldspar, enstatite, and metallic iron (Figure 35.8; see also Figure 34.7). In the differentiating earth, the present structure, with core, mantle and crust, developed during the first 500 million years. Differentiation occurred on the basis of density and melting point. Volatiles such as hydrogen, helium, sodium, potassium, lead, mercury, and zinc, with low melting points, accumulated in the outer parts of the earth and were partially swept away by the solar wind. Iron and other ferrous elements condensed under the force of gravity and started to accrete in the core. At a later stage, high-temperature silicates and oxides crystallized and accreted as a primitive mantle. Earth minerals have been forming for the last 4.7 billion years in various stages, the oldest rocks having been dated at 3.8 billion years. During an early protoplanet stage the list of minerals included about 40--50 species, corresponding largely to minerals in the oldest metallic meteorites and in primitive chondrites: enstatite, hypersthene, pigeonite, olivine, taenite, kamacite. At the basalt stage, when the mantle was accreted and started to cool, minerals typical of basaltic magmas began to form in the earth, as well as on the moon and presumably other planets. The major new mineral species that appeared were feldspars. The mineralogical composition of this early earth’s mantle corresponded closely to rocks of the moon, particularly: Major minerals ( > 10%): pyroxenes, plagioclase, olivine, ilmenite Secondary minerals (1--10%): cristobalite, tridymite, pyroxferroite At the beginning of the development of the crust there were no more than 200—300 minerals occurring in the earth. Over time, the environment became more complex; iron—nickel concentrated in the core under gravitational differentiation, the core and mantle degassed, and water appeared, first as fresh water and later accumulating in saline oceans. In the early stages there was an oxygen deficiency. Only after the formation of an oxygen-rich atmosphere by photosynthesis did new mineral species crystallize, most notably iron oxides and hydroxides of the Early Precambrian banded iron formations, as well as siliceous sediments. Crystallization of feldspars, micas, and quartz would later take place in granitic magmas. Surface minerals as well as diagenetic alterations added chlorites, serpentine, kaolinite, hematite, carbonates, and halides.
Wenk Bulakh, 2013
Two tendencies are observed in this evolution. First, in similar geological conditions the number of minerals increases from older to younger rocks. Second, the chemical composition of minerals and their crystal structures becomes more complex with the evolution of a differentiated crust. Nevertheless, by about the Late Precambrian, most of the minerals that we know of today probably already existed. Some of the important mineral-forming environments are summarized in Figure 35.4. The interaction of the convective mantle and the crust is the source of the major volcanic rocks, either during upwelling at ridges producing basalts, or during subduction with the formation of island arcs and remelting of andesitic material. Volcanism also occurs at hot spots. In the USA, alkali basalts in Hawaii and Yellowstone National Park are oceanic and continental examples, respectively. Plate divergence on continents often produces complex igneous activities, generally with alkaline rocks such as syenites and carbonatites, as in the Kola Peninsula (Russia), the Rhine Graben (Germany), and the East African Rift. Mantle convection is also the driving force for tectonic activity and associated metamorphism: convergence of plates may produce subduction that results in high-pressure metamorphic rocks such as blueschists (containing glaucophane, jadeite, and aragonite) and ultimately eclogites (with omphacite and pyrope). Where granites intrude into country rock, contact metamorphism produces skarns and hydrothermal activity with typical minerals, garnet, vesuvianite, and epidote. During crustal shortening, overthrusting with regional metamorphism causes amphibolites, gneisses, and marbles to form. Topographic elevation changes and the influence of water and ice cause original minerals to erode and dissolve; ultimately, they are transported to more stable settings. These dissolved and retransported minerals form the basis of sedimentary minerals such as clays, cristobalite--quartz, and calcite, which crystallize in lakes and oceans and are often associated with organisms. In humid tropical environments, supergene alteration of silicate rocks may occur and transform them to hydroxides (bauxite, goethite--limonite, manganese minerals) and clays (kaolinite).
Wenk Bulakh, 2013
H miatt reduktív
Anderson, 2007
Kondenzációs sorozat
Anderson, 2007
Refrakter
Highly
>1300 K
Anderson, 2007
A Föld
A Föld belső övei. A külső merev litoszférát a szilárd, de képlékeny („gyenge”) asztenoszféra követi, majd a mezoszféra ismét ridegebb. Az alatta lévő külső mag folyékony, majd a belső mag – bár kémiai összetétele hasonló a külső magéhoz - az óriási nyomás miatt szilárd. A litoszférán belüli kéreg kontinentális és óceáni kéregre tagolható.
