There is evidence that, in the early Earth, a considerable diversity of hydrocarbons produced endogenously or delivered by meteorites, comets and IDPs, could be presents on its surface, in the atmosphere and hydrosphere (Kvenvolden et al. 1970, Deamer et al. 1989, Chyba & Sagan 1992, McCollom et al. 1999). The formation of such hydrocarbons may be explained by the occurrence of Fischer-Tropsch-type (FTT) reactions (Ferris 1992, McCollom et al. 1999), mainly during the condensation of the solar nebula near 10 AU (Anders et al. 1973, Fegley & Prinn 1989, Gaffey 1997). Other pathways are thermal decomposition of iron oxalate (McCollom & Simoneit 1999) and structurally non-selective Miller-Urey (free radical) reactions (Lasaga et al. 1971, Sagan & Chyba 1997). Particularly Miller-Urey reactions yield tholin-like compounds having mainly saturated, aliphatic and polycyclic aromatic hydrocarbons (Sagan & Khare 1971, Clarke & Ferris 1997, Cleaves & Miller 1998). This paper shows the-probable amounts of the heavy n-alkanes accumulated on the Earth at the time (t) from calculation based in the contribution of organic material by endogenous and exogenous sources.