Before MCU began, there was another universe. This universe was put into sig singularities: the infinity stones. When the MCU Universe was created, these infinity stones where created. Hence why they are so powerful. When the universe began, the Celestials arrived on earth to start experimenting and create life. The eventually created the Eternals, and also left traces of their DNA in the soil of the earth, modifying the human DNA, creating the X-Gene. Since the Infinity Stones are so powerful, when snap with them in the Infinity Glove, they create cosmic energy. Having snapped 3 times in the space of years, this created a lot of cosmic energy on a large scale, activating everyone’s X-Genes on the whole planet. The Celestials will wipe out the whole earth, if they determine the new race to be unsuccessful.
Eternals are a race of immortal beings created by the Celestials to protect humanity from the Deviants.
Sersi has the ability to manipulate non-sentient matter.
Ikaris has the ability to fly and shoot beams of light from his eyes.
Kingo has the power to manipulate energy with his hands.
Phastos is a brilliant inventor with a mind for creating weapons and technology.
Sprite creates illusions to trick her foes and sometimes her friends.
Makkari has superspeed and is the fastest woman in the universe.
Druig can use cosmic energy to control the minds of humans.
Gilgamesh is capable of projecting a powerful exoskeleton of cosmic energy.
Ajak can genetically able to heal Humans and Eternals alike from injuries and illnesses.
Thena has the ability to use cosmic energy to form any handheld weapon she can think of.
All Eternals posses: strength, durability, speed, agility, stamina, reflexes, and other capabilities far superior than any human, as well as immortality. They are also able to use cosmic energy to grant themselves a special ability.