The prehistoric period during which the Palaeolithic civilisations existed in the Tamil Nadu region has been estimated to span the period from about 50,000 BCE until around 3000 BCE. For most part of the lower Palaeolithic stage, humans lived close to river valleys with sparse forest cover or in grassland environments. The population density was very low and so far only two localities of this lower Palaeolithic culture have been found in south India. One of these is in Attirampakkam valley in the northwest of Chennai in Tamil Nadu. Archaeological research has uncovered evidence of fossil remains of animals and primitive stone implements around the northern Tamil Nadu that could be dated to belong to around 300,000 BCE. Humans in South India, belonging to the species of "Homo erectus", lived in this primitive 'old stone age' (Palaeolithic) for quite a long time, using only crude implements such as hand axes and choppers and subsisting on food he hunted and gathered instead of actively growing it according to his needs.