Source of all living matter

"'When she was a girl... our ancestor Ymir Fritz touched the source of all living matter.' There are some who say that, too. There is no such thing as truth in this world. That is our reality."

- Eren Kruger speculates on the origin of Ymir's power

The "source of all living matter" (有機物の起源) is the tentative name attributed to the anomaly which granted Ymir Fritz the Power of the Titans two-thousand years ago.

Properties
While it is unknown whether or not the "source of all living matter" is indeed the origin of all life on Earth, it is evidently capable of dramatically affecting organic life in its immediate vicinity. A tree which stood over the anomaly in ancient times grew to immense proportions compared to the surrounding flora. Physical contact between Ymir Fritz and the anomaly caused the creation of the Power of the Titans and subsequent connection of living and dead consciousness in the Eldian race through the paths.

While the anomaly appears sedentary in nature, it has demonstrated some level of physical initiative, actively reaching its limbs towards Ymir as she approached and later materializing out of Eren Yeager's corpse to reconnect his body to his severed head.

History
While fleeing from her Eldian tormentors, Ymir Fritz encountered the life-giving anomaly beneath a colossal tree in the wilderness. Upon physical contact, she was imbued with the Power of the Titans, gaining the immense form of the Founding Titan.

Return to Shiganshina arc
In his journals, Grisha Yeager recounts his conversation with Eren Kruger in which Kruger elaborates on the varying stories surrounding Ymir and the origin of the Titans. While some consider Ymir's power to be of the devil and others believe her power was a gift from God, Kruger notes that some believe the origin of Ymir's power was the "source of all living matter," though he admits all explanations of such history are ambiguous and ever-changing.

War for Paradis arc
While attempting to come into contact with Zeke Yeager to unlock the power of the Founding Titan, Eren is decapitated by a shot from an anti-Titan rifle wielded by Gabi Braun. Regardless, their contact is achieved and sends the consciousnesses of the two brothers into the paths with Ymir where Eren witnesses the origin of Ymir's power. Upon gaining control of the Founding Titan, the anomaly manifests in Eren's corpse and reattaches his head to his body.

Gabi Braun witnesses this event and later recounts it to her comrades many days later, comparing the anomaly to a "shining centipede". Suspecting the anomaly to be the true nature of the Power of the Titans, Gabi anticipates seeing the anomaly once again if Eren were decapitated a second time.