The nuclei of the lithium isotopes are fragile , easily destroyed , so that , at variance with most of the other elements , they can not be formed in stars through steady hydrostatic nucleosynthesis .

The ^ { 7 } Li isotope is synthesized during primordial nucleosynthesis in the first minutes after the Big Bang and later by cosmic rays , by novae and in pulsations of AGB stars ( possibly also by the \nu process ) . ^ { 6 } Li is mainly formed by cosmic rays .
The oldest ( most metal-deficient ) warm galactic stars should retain the signature of these processes if , ( as it had been often expected ) lithium is not depleted in these stars .
The existence of a ” plateau ” of the abundance of ^ { 7 } Li ( and of its slope ) in the warm metal-poor stars is discussed .
At very low metallicity ( [ Fe / H ] < -2.7 dex ) the star to star scatter increases significantly towards low Li abundances .
The highest value of the lithium abundance in the early stellar matter of the Galaxy ( log \epsilon ( Li ) = A ( ^ { 7 } Li ) = 2.2 dex In the literature the lithium abundance , is noted indifferently by log \epsilon ( Li ) , or by A ( Li ) ; both notations are in logarithmic scale of number of atoms where log \epsilon ( H ) = A ( H ) = 12 ) is much lower than the the value ( log \epsilon ( Li ) = 2.72 ) predicted by the standard Big Bang nucleosynthesis , according to the specifications found by the satellite WMAP .
After gathering a homogeneous stellar sample , and analysing its behaviour , possible explanations of the disagreement between Big Bang and stellar abundances are discussed ( including early astration and diffusion ) .
On the other hand , possibilities of lower productions of ^ { 7 } Li in the standard and/or non-standard Big Bang nucleosyntheses are briefly evoked .

A surprisingly high value ( A ( ^ { 6 } Li ) =0.8 dex ) of the abundance of the ^ { 6 } Li isotope has been found in a few warm metal-poor stars .
Such a high abundance of ^ { 6 } Li independent of the mean metallicity in the early Galaxy can not be easily explained .
But are we really observing ^ { 6 } Li ?