S U M M A R YThe 430 km long DSS Baltic profile in SE Finland runs through the Rapakivi intrusion, the Svecokarelian geosynclinal complex, including the Ladoga-Bothnian Bay zone, and the Archean basement complex. A brief description of field operations in 1982 is presented. Record sections of P-and S-waves were used for the interpretations. A starting model was constructed by inverse methods and improved by dynamic ray tracing modelling. Three blocks are indentified on the cross-section from SW to NE. These are the southern, associated with the Rapakivi Massif, depth to Moho (M) about 40 km; the central, Ladoga-Bothnian Bay zone, with M of approximately 55-60 km, and the northern, Archean crystalline basement, with M about 40-45 km. The average crustal velocity is 6.6-6.7 kms-'. The crustal structure along the Baltic profile is compared with the surrounding DSS profiles, Finnish Sveka and Soviet Kern-Tulos and Ladoga profiles. The eastern border of the Ladoga-Bothnian Bay zone was located and specific features of the crust and uppermost mantle along the profile area are discussed.

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Abstrad-A reviewof problems related to Xe isotopicabundancesin meteorites and terrestrial materials leads to four postulates whichshould be taken into account to build a model of the Earth's accretionand early evolution. 1. The pre-planetary accretion time scale was shorter than the 129{ half-life, 17 Ma, so the initial ratio of 129y 1271 bad not been decreased considerably when planetary accretion started; therefore, this must alsobe the case for the 244Pu abundance. 2. The initial relative abundance of involatilerefractory 244Pu in fIoto-planetary materials should be the same as in chondrites, that is, 244pu,t238U = 0.0068; this value corresponds to initial 2 Pu a 0.30 ppb in the bulk silicate earth. In contrast, I is a highly volatile element; its initial abundance, accretion history and even the present-daymean concentrationsin principalterrestrial reservoirs are~rly known. 3. There is much less fissionXe in the upper mantle,crust,and atmosphere tban is predictablefrom the fission of 2 Pu (Xe(Pu» based on the above argument. Therefore, Xe(Pu) has been mainlyreleased from these reservoirs. 4. A mechanism for Xe(Pu) escape from the complementary upper mantle-crust-atmosphere reservoirs, for example, atmospheric escape via collisionsof a growingEarth with large embryosand/or hydrodynamic hydrogenflux, etc., operated duringthe Earth's accretion.These postulates have been used as a background for a balance model of homogeneous Earth accretion which envisages: growth of the Earth due to accumulation of planetesimals; fractionation inside the Earth and segregation of the core; degassing via collision and fractionation; and escape of volatilesfrom the atmosphere. During the post-accretion terrestrial history, the processesdescribed by the model are continuousfractionation, degassingandrecycling of the upper mantle and crust. The lower mantle is considered as an isolated reservoir.Depending on the scenario invoked, the accretion time scale varies within the limits of 50-200 Ma. In the light of recent experimentaldata, the latter value is inferred to the most realisticversionwhich explains a high Xe(U)/Xe(Pu) ratio in the upper mantle. Contrary to previoussuggestions, the 1291_129Xe subsystem is consideredto be meaningless with regard to the terrestrial accretion time scale. The terrestrial inventoryof 129xe(l) is controlled by the initialabundanceof volatile elements (includingI and Xe) in proto-terrestrial materials and the subsequentdegassinghistoryof the Earth.The residence time of a volatile element (e.g., Xe) in the bulk mantle (bm) duringaccretion, , is approximated by the ratio of "" IIlbm(t)/tPbm,mf S 10 Ma, where IIlbm(t) is the mantle mass, and tPbm,mf is the rate of metal/silicate fractionation, whichprovided segregation of the core; tPbm,mfis determined by involatile siderophile element abundances in the upper mantle. This relationship implies a link between the abundance of involatile siderofhile and volatile incompatible elements. A short reflects a highdegassing rate due to...