『Abstract
　Concentrations of organic acids in prebiotic soils were presumably low, given limitations in abiotic synthesis and the limited lifetimes of organic molecules before the ultraviolet shield developed on early Earth. Prokaryotes, the first land-colonizing organisms, commonly secrete aliphatic carboxylic acids, and, less extensively, secrete aromatic compounds as siderophores and antibiotic. In contrast, secretion of aromatic acids is considerable for fungi, lichens, and vascular plants. Aromatic acids are also produced by degradation oh high-molecular-weight compounds from lignin and tannin, both abundant in vascular plants. The proportion of aromatic carboxylic acids in soil solutions therefore probably increased with the evolution of higher order organisms. As biomass of organisms increased over geological time, concentrations of organic acids in soil solutions and, in turn, the extent of ligand-promoted dissolution of minerals probably increased.
　To elucidate the contribution of ligands during weathering on early Earth, Columbia River basalt was dissolved under oxic and anoxic conditions in the presence (0.001 or 0.01 M) and absence of several organic ligands in batch experiments at pH 6. Release of all elements including Si was enhanced considerably in the presence of organic ligands. Citrate (tridentate) and gallate (tetradentate) increased element release to the greatest extent among the aliphatic and aromatic ligands, respectively. The extent of element mobilization observed for the aliphatic ligands decreased in the order: citrate＞oxalate≒malonate, and for the aromatic ligands: gallate＞salicylate≒phthalate. The effects of the ligands generally followed trends in cation-ligand stability constants, but aromatic ligands were less effective in element mobilization than aliphatic ligands. One exception was gallate, an aromatic ligand, which significantly enhanced Cu release. Ligand-promoted mobilization of Cu may therefore have increased over geologic time with the increase in the proportion of aromatic ligands.
　In the presence of organic ligands, Fe was mobilized from basalt considerably more than Al even under oxic conditions. Complexation of Fe with organic ligands may have mobilized Fe in Precambrian paleosols where little Al mobility is observed. Extent of P and Y release was minor in ligand-free experiments and considerable with ligands regardless of PO2. Release of Cu was considerable under oxic conditions, especially with ligands, and minor under anoxic conditions. Mobility patterns of P and Y could thus possibly serve as “organomarkers” (indicative of prevalence of organic ligands in soil solutions) and mobility patterns of Cu could possibly serve as “oxymarkers” (indicative of the presence of molecular oxygen), respectively, in ancient soils.』

Introduction
Evolution of moieties of organic acids
　Abiotic synthesis
　General overview of biological evolution
　Secretion of LMWOA by Prokaryotes
　Secretion of LMWOA by fungi and lichens
　LMWOA in plant root exudates
　LMWOA as degradation products of HMW compounds
　Summary of the evolution of organic acid moieties
Statement of objectives
Materials and methods
　Organic ligands
　Starting materials
　Batch dissolution experiments
Results and discussion
　Solution chemistry
　Rate of dissolution
　Ligand trends
　Mobility of Si
　Order of element release
　Zr mobility
　Implications of Fe and Al mobility patterns
　Interpretations of P, Y and Cu mobility patterns
　Cu, P, and Y in paleosols
　Cu mobility over geologic time
Conclusions
Acknowledgments
Appendix 1
Appendix 2
References

Table 2 The chemical formulae of aliphatic carboxylic acids discussed in the text
本文で議論される脂肪族カルボン酸の化学式

Acid name	酸の名称	Chemical formula*	Number of C atoms
Acetic	酢酸	CH3COOH	2
Aconitic	アコニット酸	HOOCC=[CHCOOH]CH2COOH	6
Butyric	酪酸	CH3(CH2)2COOH	4
Citric	クエン酸	HOC[CH2COOH]2COOH	6
Formic	ギ酸	HCOOH	1
Fumaric	フマル酸	HOOCCH=CHCOOH	4
Glutaric	グルタル酸	HOOC(CH2)3COOH	5
Glycolic	グリコール酸	HOCH2COOH	2
Glyoxylic	グリオキシル酸	OCHCOOH	2
Isocitric	イソクエン酸	HOOCCH2CH[COOH]CH[COOH]OH	6
2-ketogluconic	2-ケトグルコン酸	HOOCC[O](CH[OH])3CH2OH	6
α-ketoglutaric	α-ケトグルタル酸	HOOC(CH2)2C[O]COOH	5
Lactic	乳酸	CH3CH[OH]COOH	3
Malic	リンゴ酸	HOOCCH2CH[OH]COOH	4
Malonic	マロン酸	HOOCCH2COOH	3
Oxalic	シュウ酸	HOOCCOOH	2
Oxaloacetic	オキサロ酢酸	HOOCC[O]CH2COOH	4
Propionic	プロピオン酸	CH3CH2COOH	3
Pyruvic	ピルビン酸	CH3C[O]COOH	3
Succinic	こはく酸	HOOC(CH)2COOH	4
Tartaric	酒石酸	HOOC(CH[OH])2COOH	4
Valeric	吉草酸	CH3(CH2)3COOH	5
* [ ] represents branched group and = represents double bond.

Table 3 The structures of aromatic carboxylic acids discussed in the text^*
本文で議論される芳香族カルボン酸の構造

Acid name	酸の名称	Moiety**（成分）
		1	2	3	4	5
Benzoic	安息香酸	COOH	H	H	H	H
Caffeic	コーヒ酸（カフェー酸）	CH=CHCOOH	H	OH	OH	H
Cinnamic	肉桂酸（桂皮酸）	CH=CHCOOH	H	H	H	H
p-Coumaric	p-クマル酸	CH=CHCOOH	H	H	OH	H
Ferulic	フェルラ酸	CH=CHCOOH	H	OCH3	OH	H
Gallic	没食子酸	COOH	H	OH	OH	OH
p-Hydrobenzoic	p-ヒドロ安息香酸	COOH	H	H	OH	H
Phthalic	フタル酸	COOH	COOH	H	H	H
Piscidic		R1***	H	H	OH	H
Salicylic	サリチル酸	COOH	OH	H	H	H
Syringic		COOH	H	OCH3	OH	OCH3
Terephthalic	テレフタル酸	COOH	H	H	COOH	H
Vanillic	バニリン酸	COOH	H	OCH3	OH	H
* The structures of lichen acids (polyphenolic compounds) are complex and thus are not shown. They are discussed, for example, in Huneck and Yoshimura (1996). ** = represents double bond. *** R1 represents CH2C[OH][COOH]CH[OH]COOH where [ ] represents branched group.