From Halopedia, the Halo wiki
The planet's equator is covered by an immense forest of spiny, vine-like trees. Its native wildlife includes Eiyaa-Mahtuhaas a species of large, presumably carnivorous quadrupedal creatures; several specimens of these creatures were kept at the UNSC facility located on the planet.
The planet's atmospheric composition makes Erebus VII habitable for humans, though extremely hostile indigenous wildlife has prevented the world from becoming a viable candidate for full colonization. Additionally, the interference of the UNSC's Office of Naval Intelligence have also prevented the consideration; ONI has established numerous facilities on the planet, though their research goals have remained unannounced.
In 2557, ONI lost contact with its research teams and the planet's facilities were left abandoned. Several remote contact teams were sent to determine the cause of contact loss, but they only found empty laboratories and were unable to determine the location of its staff. Research on Erebus VII has since been suspended by the Office of Naval Intelligence, and there is no plans to commit new resources. A War Games simulation of the abandoned facility was later used by UNSC Infinity's SPARTAN-IV complement for training. The scientists had been studying the anglers that inhabited the planet and captured a nest of very young juveniles. The anglers proved to be an intelligent species and started hunting them in turn. At that point, the scientists performed horrible experiments on the captured juveniles. In one night, the scientists lost dozens of people to the anglers in a coordinated attack. Using their light and mimicry, the anglers lured the survivors in and killed many of them until they realized that the humans were no longer falling for it and moved on to systematically removing and destroying their satellite uplinks, comms stations and power cores. A few months later, the ONI teams showed up and became the target of the anglers.
In August 2558, Rion Forge was sent to Erebus VII through a slipspace portal from Installation 07. After getting captured by the anglers, Rion was rescued by the survivors on an ONI team that had been investigating the disappearance of the researchers and the two surviving researchers that they had found who explained what had happened to them. After retrieving the third piece of the coordinate key from a Forerunner way station on New Carthage, 343 Guilty Spark was led to Erebus VII where he rescued Rion, the survivors she'd found and four more located elsewhere on the planet. The Ace of Spades then delivered the survivors of Erebus VII to a mining outpost in a nearby star system. Spark later suggested that the anglers may have been seeded on Erebus VII, designed or modified, to dissuade visitors to the planet and to protect the Forerunner site there.
After dropping off the survivors, Spark and Rion returned to Erebus VII and used the completed coordinate key on a terminal in the Forerunner facility. The Precept appeared and tested Rion. Upon being satisfied, he imbued the coordinate key with the coordinates to a portal to Bastion and access permissions for Spark and Rion.
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