Tallon IV was a biological paradise that was colonized by the Chozo prior to the impact of a Leviathan from Phaaze. What remains of the planet's once rich biosphere began slowly fading due to exposure to Phazon radiation.
Tallon IV's ecosystem faced complete obliteration in the face of intense radiation following a meteor impact. When she arrived on the planet, Samus Aran estimated that in approximately 25 years the contamination would turn Tallon IV into a barren Class XIII wasteland.
The planet is in the same solar system as Oormine II, Twin Tabula, Bilium, and Zebes, and can be scanned along with them via the Astronomical Holographic Projector in the Observatory of Phendrana Drifts. It has a mass of 5.1 trillion teratons, just slightly smaller than Earth.
 Chozo Colonization
The Chozo that colonized Tallon IV made a conscious choice to eschew a civilization of advanced technology and build their colony out of unprocessed natural materials, so that it would be harmonious with its surroundings. The Chozo believed that through harmonious coexistence with their surroundings, and ultimately with the universe, they would gain a better understanding of their existence and the nature of the universe. Gradually they gained the power to see into the future, which they interpreted as a sign of their "burgeoning harmonization with the infinite."
 Meteor Impact
Unforeseen by the Chozo, a Meteor impacted the planet and left a Great Poison in the wake of its devastation. The Chozo speculated about the nature of the Leviathan, considering the possibility that it was crafted by alien hands or that it was in fact a part of a planet. The Chozo go as far as suggesting that somewhere in the universe there may be or may have been a planet covered in Phazon. Phaaze is that planet, although it wasn't revealed until the events of Metroid Prime 3: Corruption.
As time passed the Chozo began to understand the severity of the disaster. They chose to build a temple to contain the Phazon and stop it from poisoning more of the planet. Even though they had given up hope to see the day the Phazon was eradicated themselves, they believed that a savior would come to aid their world one day. They left behind tools and weapons for their savior to find so that their work could be completed. They foresaw the coming of Samus Aran in a vision prior to their destruction.
 Releasing the Cipher
A massive energy spike emanating from Tallon IV attracted Space Pirates, who discovered Phazon there and began analyzing its potential as a viable secondary headquarters. Following their defeat on Zebes, they began conducting experiments on Metroids and species native to Tallon IV. They constructed their main Research Headquarters in the planet's mountainous region and hosted a series of research projects there, and began extensive mining operations of the planet's Phazon. Parasite test subjects on board their research frigate Orpheon escaped and forced the crew to evacuate. This incident ultimately drew Samus Aran to Tallon IV, as she approached the planet in response to their distress signal.
Meta Ridley managed to escape the destruction of the frigate and fled to Tallon IV, prompting Samus to follow. Upon arriving she discovered the remains of the Chozo civilization, including their Temple built to contain the destructive meteor impact, the mutagenic substance Phazon and victims of its effects, and the Space Pirate establishments. Samus manages to severely disrupt the Space Pirate operations, reassemble the Cipher left behind by the Chozo, and destroy the source of the Phazon in the Impact Crater, Metroid Prime, halting the planet's decay.
 Topography and Ecosystem
Tallon IV has diverse geography and climate, ranging from frozen drifts to volcanic caverns, and each has its own unique biosphere of herbivores, scavengers, and predators. While some areas have been completely devastated as a result of Phazon exposure, others are less effected.
The colonized portion of the planet is divided into six main explorable areas, including the site of the meteor impact that brought Phazon to Tallon IV.
 Tallon Overworld
- Main article: Tallon Overworld
The Tallon Overworld is the rainforest continent where Samus first arrives, host to a plethora of local plantforms, fungi, and wildlife. It is the site of the Artifact Temple, the great Cradle of the Chozo, and consequently the only area from which Samus can access the Impact Crater. The natural predators here pose no real threat to Samus as she explores, incurring minor damage during confrontations.
 Chozo Ruins
- Main article: Chozo Ruins
The Chozo Ruins are the location of the first area of Tallon IV first colonized by the Chozo. Most of the lore left behind by the Chozo can be found here, as well as multiple upgrades for Samus's arsenal. This location is one of those hit hardest by the devastation of the meteor impact; water sources are poisoned and some local life-forms have undergone severe mutation.
Hauntings by spectral entities here known as Chozo Ghosts led to several casualties for Space Pirates who were studying the Ruins for their own gain.
 Magmoor Caverns
- Main article: Magmoor Caverns
The Magmoor Caverns are a subterranean network of lava-filled caves, so named because of the large local predators of this habitat, the Magmoors. Because of the abundance environmental hazards, the Spider Ball and Grapple Beam upgrades are utilized often here.
Chozo Statues evidence the remains of Chozo colonization here, but most unnatural structures here are the result of Space Pirate geothermal processing operations.
 Phendrana Drifts
- Main article: Phendrana Drifts
The frozen Phendrana Drifts are home to the fearsome Sheegoth, a dangerous local predator. There are also several Chozo religious sites here.
The Space Pirates set up multiple research bases here and still inhabit the area when Samus arrives. Among the Phazon experiments conducted here was the failed Project Titan, one specimen of which ended up being too aggressive for the Space Pirates to tame, resulting in the abandonment of the project; they immobilized the test subject in the Quarantine Cave, where Samus engages it in battle.
 Phazon Mines
- Main article: Phazon Mines
The Phazon Mines are an advanced mining facility installed on Tallon IV by the Space Pirates when they discovered the potential of Phazon as a power source.
In addition to harvesting raw Phazon ore here, they also conduct various experiments with Phazon mutations, including inducing gigantism in local fungi, Phazon injection into Metroids, and the infamous Project Helix, which resulted in the powerful Elite Pirates and Omega Pirate.
 Impact Crater
- Main article: Impact Crater
The Impact Crater is the final section of Tallon IV that Samus explores in Metroid Prime. It is only accessible after Samus collects all twelve Chozo Artifacts scattered across the planet and she defeats Meta Ridley at the Artifact Temple.
This place is full of Orange Phazon, a highly concentrated form of Phazon that damages Samus even through her protective Phazon Suit. It is also inhabited by Lumigeks and Fission Metroids, and is where the Leviathan polluting the planet and Metroid Prime had landed some fifty years before Samus arrived.
- "Scans of the Spiral Sector detected a massive energy spike emanating from a Wanderer-class planet identified as Tallon IV." —Space Pirate Data "Contact" (Metroid Prime)
- "Planet Tallon IV. Mass: 5.1 trillion teratons. Profile: Ecosystem studies indicate that Tallon IV was a biological paradise prior to the impact of an extraterrestrial object. What remains of the biosphere is slowly fading due to exposure to Phazon radiation. At current rate of decay, Tallon IV will be a barren Class XIII wasteland in approximately 25 years." —Metroid Prime Logbook "Tallon IV" (Metroid Prime)
- "The history of the Chozo stretches back into ancient times, so far into the fog of the past that we know not where our ancestors came from. One thing is clear, however: the Chozo who colonized Tallon IV made a conscious choice to eschew a civilization of advanced technology. They chose to live in harmony with nature, guided by the providence of the universe. As this city grows, we plan to honor them with written tributes, carvings etched in stone to remind us always of their legacy." —Chozo Lore "Beginnings" (Metroid Prime)
- "We know not how the ability has come to us, but recently many Chozo have begun to sense things beyond the realm of ordinary perception. Strange sights and inexplicable sensations flood our minds, filling us with visions of past and future. We take this growing ability to be a sign of our burgeoning harmonization with the infinite; perhaps, finally, the universe's secrets are becoming known to us." —Chozo Lore "Harmonization" (Metroid Prime)
- "Many Chozo are gifted with the distant sight, and even more begin to learn it as our harmonization with the universe becomes more and more complete. We peer forwards, seeing prophecy in the ripples of the water, hearing rumors of coming days on the breath of the wind. Though we celebrate the distant sight, many of these visions are dark - the worst of the prophecies, and the most common, tells of the coming of the Worm. Born from parasites, nurtured in a poisoned womb, the Worm grows, devouring from within, until the world begins to rot. Not all prophecies come to pass, of course, but we cannot help but fear this dark portent." —Chozo Lore "Worm" (Metroid Prime)
- "Unforeseen by sages, a meteor came as if from nowhere, casting a dark shadow of debris over the land with the violence of its impact. Its destructive force spent, the fallen star burned itself out rapidly, and the incident should have faded into memory...but the meteor brought with it corruption. A Great Poison burst forth into the land, a strange energy that clawed at natural life with a ferocity that seemed almost sentient. Bound by our ignorance of this phenomenon, we Chozo could only watch in horror as this dark force slowly began to spread across the surface of Tallon IV." —Chozo Lore "Meteor Strike" (Metroid Prime)
- "What is this otherworldly pestilence that infests the land, seeking out life in its blind need for corruption? And where did the meteor that brought it originate? Was it crafted by alien hands or is it a roving chunk of a planet that suffered a violent end? Our minds quail in horror at the thought that long ago, in some corner of the universe as yet unseen by our eyes, an entire planet was perhaps once coated with this Great Poison. Whatever cataclysm may have ruptured that doomed place must have been mighty, indeed...and if other meteors from it spread through space, bearing this evil to the far corners of the universe... We hold fast to the hope that this is not so, that the only surviving remnants of this evil are here, on Tallon IV. Then, at least, there is hope for its eradication." —Chozo Lore "Great Poison" (Metroid Prime)
- "None know if our temple, the Cradle, will prove powerful enough to contain this evil forever. For now, it wraps around that abomination, cutting it off from the world above. But how can we Chozo hope for the Cradle to remain intact when that which it guards writhes in the darkness, growing always stronger? The fate of this world rests with the gathering of Artifacts we call the Cipher, but even it is not all-powerful. It is strong, yes; an enchanted whole made of twelve links. Still, it is finite in its reach, and we who guard it are slowly succumbing. Will the Entrusted One arrive before our vigilance crumbles away? That time rapidly approaches..." —Chozo Lore "Cradle" - PAL version (Metroid Prime)
- "The power of our temple has been enough to halt the spread of the poison on Tallon IV, but whether the evil can ever be truly destroyed is not for our eyes to see. The future is cloudy to us, a world of veils where dark apparitions flit in the shadows. Within this strange world, one image stands out in the mist, flickering through the landscape, wraithlike. It is a human, a lone figure shining in the toxic shadows. We Chozo do not know what it is, but our hearts swell with hope at the promise of that glowing light. We will place our faith in our shrine; we will be there when the light shines upon our land." —Chozo Lore "Shining One" (Metroid Prime)
- "We believe that on some far-off day, a savior will come and continue what we have begun. For that savior, we will leave our ancient weapons and armor - the soul who can gather them will be the Entrusted One, the only being who can reverse the evil that grows here." —Chozo Lore "Entrusted One" (Metroid Prime)
- "Planet Tallon IV, formerly a Chozo colony, was struck by a stellar object 50 years ago. Object was later determined to contain large quantities of Phazon. The Chozo were able to stave off the spread of Phazon, at the cost of many Chozo lives. The survivors abandoned the planet, fleeing to an unknown location. Decades later, Hunter Samus Aran responded to a distress call in the sector and discovered a Space Pirate Phazon Mining Station there. Aran eliminated both the pirate and Phazon threat from the planet, though not without cost." —Galactic Federation Data "Tallon IV Incident" (Metroid Prime 3: Corruption)
- "Scans of the Spiral Sector detected a massive energy spike emanating from a Wanderer-class planet identified as Tallon IV. Scout reconnaissance was immediately dispatched to the center of the spike, a land mass at heading mark 40.08.02, returning with planetary samples and atmospheric imaging. Analysis shows the energy source to be an unstable radioactive material of enormous potential. We are unable to form an accurate risk-assessment at this time, but we are unlikely to find an energy source this powerful again. Analysis will continue, but currently Tallon IV appears to be a viable secondary headquarters." —Pirate Data "Contact" (Metroid Prime)
- "Zebes has fallen. All ground personnel are presumed dead, either killed by the Hunter clad in metal or in the subsequent destruction of the underground facilities. Our research frigates Orpheon, Siriacus and Vol Paragom were in orbit at zero hour and managed to retreat. Frigate Orpheon is now docked at Vortex Outpost. Orpheon's cargo appears to have a 100% survival rate; Metroids are healthy but on restricted feeding schedules due to uncertain supply status. We are ready to begin research on the Metroids and other promising life-forms. Security status remains at Code Blue; no signs of pursuit from the Hunter." —Pirate Data "Fall of Zebes" (Metroid Prime)
- "Tallon IV appears to be a utopia for biological life, containing an oxygen-rich and hospitable atmosphere. The planet is home to countless species of flora and fauna. Satellite scans detect numerous structures on the planet's surface, with closer examination revealing many of these structures to be of Chozo origin. Tallon IV's scar, the result of a celestial body impacting the planet's surface decades ago, is still visible. Satellite scans are unable to determine the extent of the original damage, but the planet appears to have recovered from any negative effects of the object's impact." —Metroid Prime 3: Corruption Logbook "Planet Tallon IV" (Metroid Prime 3: Corruption)