After the epic war of Mahabharat, as dwapar yug gave way to kaliyug, Maharishi Ved Vyas foreseeing the devolution of society and threat to our culture, documented the gyan of Vedas in the Puranas. Amongst these Puranas, Shrimad Devibhagwat Purana details the various yugas and dharma of each yuga.
According to this text, the beings who practice dharma are born in satyug, those who are affectionate for dharma and artha take birth in tretayug, the ones who admire dharma, artha and kaam take birth in dwaparyug and the ones who only want to indulge in artha and kaam are born in kaliyug. A being is bound by the effect of kaal (time), which is determined by the prevailing yuga and behaves accordingly.
Rishi Vyas explains that men who take birth in satyug and perform punyakarmas (the roles and duties in accordance with their varna) depart to punyalokas. The same happens in dwapar and treta. But in kaliyug, due to the effect of yuga, dharma (which has satya at its foundation) deteriorates and all the four varnas – brahmins, kshatriyas, vaishyas and shudras – become devoid of dharma, and are veiled by falsehood and indulge in paapkarmas (unrighteous deeds). (Here it is important to note that Vedas do not talk of superiority of one varna over the other but simply recognizes them as different on the basis of roles performed by a particular group for ease of organization of society.) Due to their actions, these people then go to the narakloka and stay there till the yugas change. When kaliyug ends and the satyug begins, the punyaatmas take birth again as mortals on prithvilok. When dwapar ends and kaliyug begins, then all paapatmas from narakloka take birth as mortals on prithvilok.
Kaliyug is characterized by asatya as are the people who belong to this yuga. However due to daivyog (Divine will), this arrangement is sometimes varied and whatever sadhujanas are born in kaliyug are manushyas (mortals) from dwaparyug. Manushyas from dwapar yuga are also born in tretayuga and those from treta in the satyuga. Ved Vyas details that the ones who were considered rakshsas in other yugs would be born as brahmins and gurus in kaliyug. These people would be mostly hypocrits, thugs, untruthful, who are far away from Veda and dharma. They would serve paapis, propagate many religions and criticize the Vedas. They would be brutal and mostly indulge in empty arguments. Due to the effect of kaliyug, it will be extremely difficult to find and follow a true Guru and people would find it easier to follow rakshsas instead because they too will be of asuric pravritti and possess a selfish nature. They would live for just themselves and as a result fall into greater hells because of the fruits of their karmas.
The only way to escape nark in kaliyug is to follow the true path of yog under the sanidhya of a Guru, as given in Patanjali Yogsutras without dilutions and modifications. The atmosphere in the ashram where Guru stays is unaffected by change of yugas and time flies as a sign of evolution.