The rhizome system is expanding in full force, upward, left, right, forward, and the distance has reached almost ten kilometers.

Along the way, Huogu didn't see anything like a support column, and his curiosity couldn't help but be even stronger.

"The air environment is dominated by oxygen, which accounts for 67% of the air......"

That's a staggering percentage of air, and you know, during the highest oxygen levels on Earth, oxygen only accounted for 35% of the air.

Fortunately, Hogu can adjust the cells, and when other creatures come here, they will immediately cause oxygen poisoning due to excessive oxygen inhalation.

Huo Gu observed the surrounding environment, to be honest, this super giant hollow is flat beyond Huo Gu's imagination, if you just look at a small place, it is indeed undulating, but if you look at it, it is a straight face, not like it can be formed naturally at all.

Even though Hogu's attention shifted elsewhere, the expansion of the rhizome system did not stop, and vaguely, Hogu noticed a columnar object in front of him.

Support columns?

One such thought came to Hogu's mind.

After much hesitation, Hogu did not slow down the pace of covering the rhizome system, and of course, his vigilance against the columnar object could not be relaxed, and Hogu was ready to fight at any time.

It's no wonder that Huo Gu is a soldier, in this strange environment, encountering such a strange thing, especially when he was driven into the underground hollow by some unknown creature before, Huo Gu can no longer take the earth's Underworld into it.

After a while, the pillar changed from a vertical line to a vertical column, and Hogu began to adjust the vitreous of his eyes, pointing towards the true face of the column.

However, to Hogu's disappointment, the pillar was not an entity, but a liquid, a column of water formed by the falling waters of the ocean above, and from the pool below the water column, Hogu could see sporadically floating hoists and titanium snails that had lost their ability to act on their own.

"Although these organic materials are not a blessing in disguise, the icing on the cake is not a bad thing, and with this water source, the pressure on the supply and delivery will be much less."

A cone-shaped creature soon entrenched in the water, collecting organic material from the seawater, and its rhizome continued to spread and expand forward.

This expansion continued for some time, and Hogu finally encountered the edge of this super-giant hollow, but not in front, but in the upper and left and right directions of the rhizome, reaching the edge at a distance of about a hundred kilometers.

The rhizomes that touched the edges temporarily stopped spreading and expanded, and samples of these edges were collected for analysis in situ, and the results were mixed for Hogu.

On the left and right sides are standard neutral volcanic rocks such as andesite, andesite, coarse face, and alkali long coarse rock, but above is a large metal face, which looks the same as the metal plates excavated in other cavities before, and seems to have become very rough over time.

Huo Gu immediately commanded the rhizomes on the left and right to break through the volcanic rock, and sure enough, as he continued to penetrate into the volcanic rock about a meter thick, the same metal surface appeared.

"Analyze the constituent elements of these metals, and the half-life time they go through."

Repeating what he had done in another underground cavern, Hogu got the answer—800 million years, the same time as the metal plate.

Not only the time, but also the constituent elements are the same, but there are slight differences in proportion.

"It looks like that metal plate must be part of this metal wall."

"Oh no, it's really a man-made ......"

Huo Gu pondered for a while, and then added.

“…… It could also be a comet that has landed on this planet. ”

Hogu thought of some of the comets that had been observed to cover most of their area with metal.

If it is a comet, when it enters the planet, the metal will become molten due to the friction with the atmosphere, and the comet will be completely encased, and the comet will be able to form a circular cross-section if it is still rotating at high speed when it falls.

This explanation also seems to make sense, but later discoveries make this explanation untenable.

Spreading and exploring the rhizome system ahead, it was not long before a distance of about a hundred kilometers that a rather strange place was discovered.

A cube-shaped object can be seen, as if it had been cut by hand, but it was integrated into the ground without any gaps.

Near the cube was a mound of earth, on which Hogu could see what appeared to be a round object like a wheel.

Where the cube and mound are perpendicular to each other, there are three columnar stone pillars, not connected to the dome, about half a meter in diameter and three meters in length, which look like test tubes placed upside down.

That's all there is to it, and nothing else.

Huo Gu zoomed in and looked at everything here, it was basically determined that none of this was naturally generated, and the underground cavity it was currently in was created by intelligent life.

Newhisker analyzed the material of these objects, and the half-life time was the same as that of the metal wall of the underground cavern and the metal plate excavated, but it was because of this metal material that it was able to be presented to Hogu over hundreds of millions of years.

At that cube, Hogu used his roots to clean up the dust that had clumped into rocks, and it was because of this accumulation of dust that had been accumulated for hundreds of millions of years that the cube seemed to be seamlessly connected to the ground.

After carefully cleaning up the dust blocks, Hogu retrieved several geometric shapes from the sides of the cube, and then cleaned up several other dusty objects.

After learning about the situation in the mound through the roots, Huogu basically determined that the mound was once supposed to be a means of transportation like a car, and finally could not withstand the erosion of the years, so it became the mound.

The three stone pillars, which Hogu guessed were some kind of machine, were hollow inside, with silicon accounting for one-half of them, and did not resemble the geometry that existed on the cube.

Huo Gu can roughly guess what the purpose of this machine is, people are iron and steel, and if you don't eat, you die, in this kind of desolate area where there is no village and no store, what else can this machine be except to ensure food and allow intelligent beings to continue to maintain their state of life?

As for the cube, Hogu began to speculate that it was a coffin, a sleeping pod, or something, however, the rhizome did not find a particularly noticeable gap in the cube, and there was obviously no such thing as a lid, so the speculation was overturned.

The spread of the rhizome in front of it continues, and it cannot reach the edge, and Hogu will not tell the rhizome to stop the spread.

About thirty kilometers away from the strange place, a huge square of cubes appeared in front of the rhizome group, and tens of millions of cubes were displayed there.