Hinduism, which is considered to be the oldest religion which has no founder, or single philosophy, or beliefs, but it is still practiced by over a billion across the planet, is one of the complex and has a lot of puzzles that are yet to be solved and understand by modern humans. Hinduism has a lot of holy books like
·         Vedas:  there are 4 Vedas, that has detailed information on performing different yajna’s (fire sacrifice) to please gods,
·         Upanishads: that preaches different philosophies and interpretation derived from Vedas,
·         Ramayana and Mahabharata: stories or incidents from the ancient past that sets an example that righteousness(dharma) alone wins at any situation
·          Puranas: there are 18 major Puranas that have written records of different stories or incidents from different ages.
Among the above mentioned books Puranas stand aside, though they have less prominence in Hinduism, they have a lot of in-detailed inscriptions of incidents that had occurred in the ancient past, from the beginning of mankind to the future of earth, different planets, time dilation, space travel, celestial weapons, flying machine, and more. Alongside these, they also mention different kinds/races of extraterrestrial/ aliens visiting the earth and their dominance ruling over the earth.
But before going further, let’s understand what yugas is their duration, and characteristics:
According to Vedic scriptures the years on earth is divided by 4 yugas, and by each Yuga passes the duration of time (years), righteousness (dharma), the strength, life expectancy, and fertility of life forms decreases by time:
  • Sathya Yuga = number of solar years = 1,728,000 | average human height = 33f, 6 inches | average human life span = 100,000 years.
  • Treta Yuga = Number of solar years = 1,296,000 | Average human height = 22ft 4 inches | Average human lifespan = 10,000 years.
  • Dwapara Yuga = Number of solar years = 864,000 | Average human height = 11ft 2 inches | Average human life span = 1000 years.
  • Kali Yuga = Number of solar years = 432,000 | Average human height = 5ft 3 inches | Average human life span = 100 years.
To begin with, just like any other major religions across the globe it all begins in Sathya yuga with the great flood, where lord Vishnu/Enki informs him of upcoming flood and instructs manu or Shraddhadeva, a human king to build a huge boat that housed his family, 7 sages, nine types of seeds and animals to repopulate the earth, and after the floods deluged, manu and 7 sages repopulated the earth and ruled earth for a period of time.
After a period of time, the Daityas/Danavas arrived to the earth as a result of conflicts with devas in Indra Loka, as devas cheated them in sharing of Amrutha (nectar of immortality), to showcase their comeback they conquered whole earth from human kings, which is against the law of cosmos and set their kingdom and treated humans harshly, and it was the duty of Devendra/Zeus/Ashur, who is the king of devas and also held the duty of protecting righteousness(Dharma) in the universe. And Daityas/Danavas were led by Hiranyaksha and Hiranya Kashyap, who were the grandsons of Brahma himself, and they overpowered devas. They conquered whole of known universe and to further show their vengeance on god they took planet earth away from solar system and hid it in dark cosmic oceans, and Lord Vishnu (the preserver of cosmos) took form of boar (Varaha) and carried the earth on his tusks and aligned to its original position, killed hiranyaksha and later Vishnu took avatar of Narasimha (half-human and lion) killed hiranya Kashyap, and finally Daityas/Danavas fell on earth.
varaha, avatar of vishnu lifting earth on his tusks and killing hiranyaksha

narasimha, avatar of vishnu killing hiranya kashyap

In treat Yuga, Danavas dominance fell drastically and a new race Asuras rose in power on earth, though they were not as strong as Danavas, they had a strong army of Rakshasas descended from lower worlds, asuras power was limited to ancient southern Asia and Americas and there were a lot of battles fought between humans and asuras, their prominent ruler was Ravana, who was once again a great grand-son of Brahma, he was a well-learned scholar and had a lot of celestial weapons, flying vimana's, and had total control over movements of planets in solar system, who had is capital in Lankapuri (Sri Lanka) Later Ravana was defeated and killed by king Rama of Ayodya in the battle of Ramayana. After Asuras were defeated, the Rakshasas in the army of Ravana scattered across the earth and built their independent kingdoms.
Ravana, king of lanka, and all the nine planets below his feet
In the later Dwapara Yuga, there was a lot of mess on earth, many extraterrestrial races co-existed on earth alongside humans, and there was a practice of matrimonial exchanges between humans and extraterrestrials, for maintaining peace and mutual support. And due to the war of Mahabharata in Asia, and Trojan War in ancient Greece most of the extraterrestrial races perished, and empires ruled by human kings rose.
battle of kurukshetra (Mahabharata)
According to ancient Hindu scriptures currently earth is in kali yuga which is the last of the four, where average humans life span is 100 years, and average humans height is 5ft, 3inches, and righteousness (dharma) will be followed least, and at the end of the kali yuga Lord Vishnu will take the avatar of Kalki and destroy the evil humans on earth and establish Dharma back on earth, so the earth can once again get back to Sathya yuga, where dharma is highest.