SCIENTIFIC CORRESPONDENCE

ESTIMATED HG EMISSIONS FROM FOREST BURNING IN THE AMAZON The world's 1 1 Biomass tha- Hg(µgg- ) Hg release Hg release efficiency (%) (g per ha) oldest songbird Above ground wood and litter 216 0.02 90 3.8 (roots, fallen trunks and SIR - The songbirds or passerines standing trunks) (Passeriformes) are the most speciose Above ground leaves and below ground roots 54 0.03 75 1.2 and widely distributed order of living Soil organic matter 47 0.30 20 2.8 birds, comprising about 60% of the 9,000-10,000 Recent species and occur­ Total 317 7.8 ring on all continents except Antarctica. It is not known whether the Passeriformes cient help of mycorhizae. Plant litter in mass. Thus tentative estimates of total Hg had a northern or southern origin. Tradi­ the Amazon shows lower concentrations released from deforestation during the tional, pre-continental drift views held 10 than the living leaves • Therefore I will past 20 years are useless. Finally, a signifi­ that Australo-Papuan passerines were use the same concentrations used for cant proportion of the biomass remains derived from and often confamilial with 1 trunks for this compartment. The soil intact after burning, keeping a fraction of Northern Hemisphere invaders , an organic matter Hg content used by Veiga the Hg preserved as partially burnt vege­ interpretation challenged by palaeonto­ 2 et al. is in agreement with reported values tation and as coal. logical evidence and molecular studies • for the Amazon, and their value for Using the year 1990 for comparison, These latter studies concluded that efficiency of Hg release during burning Hg emission to the atmosphere in the the many endemic Australo-Papuan seems fair. Brazilian Amazon due to gold mining passerines were part of a large-scale Recalculating the estimates of Hg ranged from 70 to 100 t (refs 2, 3). autochthonous radiation from but a few release to the Amazon atmosphere Recently, this type of mining spread ancestral types, overlaid by more recent 2 through forest burning ( see table) and throughout other Amazonian countries. northern invaders • using the deforestation rates of 1990-1991 In Venezuela, 40 to 50 t of Hg are These ideas have yet to be verified by 2 3 of 11,100 km , I obtain approximately 8.7 t released by this activity • In Colombia, unequivocally identified fossils; all pur­ for this year. Even taking the largest esti­ Peru, Ecuador and Guyana, at least 10-20 ported Eocene and Oligocene passerines 2 mates of 1978-1988, roughly 17 t of Hg t more are released annually , and more before 1989 were misidentified . The ear­ would have been emitted annually during mining fields are being opened every year. liest undoubted passerines come from that period, still four to five times lower Therefore, although deforestation is a Late Oligocene deposits in France4. The than the proposed estimate of Veiga et al. serious environmental threat to the Ama­ extensive early Tertiary sites in North Even this value is likely to be an overesti­ zon, if there is any "significant villain" in America and Europe contain many small mate, as Hg concentrations in biomass the emission of Hg to the Amazon, it is arboreal forms, most belonging to the 3 from the Amazon forest as well as in soil definitely gold mining. Coraciiformes; none is passerine • It has organic matter will probably be much Luiz Drude de Lacerda been proposed that passerines had a lower. In addition, many deforested areas Departamento de Geoquimica, southern origin, not spreading to the are now in various stages of regrowth fol­ Universidade Federal Fluminense, Northern Hemisphere until the mid-Ter­ lowing abandonment, therefore actually Niter6i, Rio de Janeiro 24020-007, tiary. Unfortunately, there is no evidence accumulating Hg in their fast-growing bio- Brazil of early Tertiary passerines in Southern 6 7 Hemisphere deposits • • An Early Eocene site from Murgon, southeastern Queens­ Origin of chondrules explained land, has now yielded material identifiable as passerine. SIR - Chondrules generally are milli­ were the product of differentiated plane­ The matrix yielding the fossils is 3 metre-sized, near-spherical stony objects tary bodies • Furthermore, Ash perpetu­ green clay, radiometrically dated potassi­ 8 that are the main constituent of the most ates a common misconception that um/argon; illite) at 54.6 ± 0.05 x 10 years • primitive types of meteorite. Many regard chondrules have "approximately solar" This age is corroborated by non-avian chondrules as having formed in a proto­ "relative abundances of refractory trace elements of the Tingamarra local fauna, planetary disk by complete or partial elements". At the conference on which which includes Australia's oldest frog, melting of nebular solids. In contrast, his article was based, after exchanges trionychid turtle, madtsoiid snake, I believe that chondrules probably result­ between several participants, it was marsupials, bat, and non-volant placental ed from interactions between already dif­ agreed that chondrites (the bulk mete­ mammal. The fossils of passerine and ferentiated, partly molten planetary orites) have approximately solar elemen­ other birds form the earliest modern, non­ 9 bodies. tal abundances but that there is "large marine avian assemblage from Australia • My view was, unfortunately, misrepre­ compositional variability of chondrules sented in the News and Views by Ash1 by from a single meteorite, reflected in 1. Mayr, E. Bull. Am. Mus. nat. Hist. 93, 123-194 (1944). 2. Sibley, C.G. & Ahlquist, J.E. Phylogeny and Classification his statement that I " ... prefer an origin major variations of Mg/Si ratios, of Al of Birds: A Study in Molecular Evolution (Yale Univ. in a modified, geologically undifferen and other refractory element abun­ Press, New Haven, 1990). 4 3. Olson, S.L. in Avian Biology, Vol. 8 (eds Farner, D.S. et tiated planetary body... ". Since the early dances ... " • al.) 79-238 (Academic, New York, 1985). 1970s, when plagioclasc glass with a plan­ The 'magic' to be explained is how 4. Mourer-Chauvin§, C., Hugueney, M., & Janet, P. C. r. hebd. Seanc. Acad. Sci., Paris (ser. 2) 309, 843-849 etary chemical signature was discovered in chemically diverse objects, chondrules, be (1989). 2 an ordinary chondrite , I have tried to they nebular or planetary, when mixed in 5. Olson, S.L. Acta XIX Congr. Int. Om. 2023-2029 (1988). demonstrate that some chondrules at least nature in gram-sized or larger amounts, 6. Vickers~Rich, P. in Vertebrate Palaeontology of Australasia (eds Vickers-Rich, P., Baird, R.F., Monaghan, always produce uniform, near solar com­ J. & Rich, T.H.) 722-808 (Nelson, Melbourne, 1991). 1. Ash, R. Nature 372, 219-220 (1994). positions. 7. Boles, W.E. in 3rd Symp. Soc. Avian Paleont. Eva/. (ed. 2. Hutchison, R. & Graham, A.L. Nature 255, 471 Peters, D.S.) (Courier Forschungsinstitut Senckenberg, (1975), Robert Hutchison in the press). 3. Hutchison, R., Alexander, C.M.O'D. & Barber, D.J. Phil. Mineralogy Department, 8. Godthelp, H., Archer, M., Cifelli, R., Hand, S.J., & Trans. R. Soc. A325, 445-458 (1988). Natural History Museum, Gilkeson, C.F. Nature 356, 514-516. (1992). 4. Palme, H. Chondrules and the Protoplanetary Disk 9. Boles, W.E., Godthelp, H., Hand, S.J. & Archer, M. (abstr.) 30 (Lunar Planet. Inst., Houston, 1994). London SW7 5B0, UK Alcheringa 18, 71 (1994). NATURE · VOL 37 4 · 2 MARCH 1995 21