The Pustlaukis pit was dug out by a steep and swirling stream of water falling from the edge of the glacier in the late ice age. The ice floe left in the pit further accentuated the shape of the relief and when it melted it turned into a rather deep lake. Relatively recently, this body of water turned into a swamp, and there are still a few small openings. The water layer under the raised bog covered in vegetation is from 4 to 6 meters.
Palynological (pollen) studies carried out in Pustlaukis pit showed how the climate and vegetation changed in this area. 11 – 12 thousand years ago, pines and birches prevailed here and grass grew abundantly; 9 – 10 thousand years ago, forests spread, and various types of grass disappeared; 8 – 9 thousand years ago aquatic vegetation was dominant there; 5 – 8 thousand years ago a sudden increase in broad-leaved trees (oaks, lindens, elms) was observed; 3 – 5 thousand years ago, dense spruce forests have formed and during the last climate cycle, which has been lasting for more than 3 thousand years, the number of pines has increased again in the environment of the Pustlaukis pit.