Sixty-seven kilometers below sea level, Wu Dong's sensory fibers detected a cavity, a very large cavity.

At the same time, a hundred fibers were dispersed, and Wu Dong probably figured out the situation of this underground bubble structure.

Mantle layer.

The term geology refers to the earth's crust below the earth's mesosphere, about 2,865 kilometers thick, mainly composed of dense rock-forming material, which is the largest and most massive layer in the earth's interior. The mantle can be divided into two layers, the upper mantle and the lower mantle. In the upper part of the upper mantle, there is a layer in which seismic waves travel at a slower rate, commonly known as asthenosphere, which is presumed to be caused by the concentration of radioactive elements, metamorphosis and exothermy, which softens the rock at high temperature and melts locally, and is likely to be the source of magma. The mantle above the asthenosphere is an integral part of the lithosphere.

The temperature, pressure, and density of the lower mantle all increase, and the matter is a plastic solid.

The detection range of 600 kilometers cannot reach the depths of the earth's mantle, and it is even farther away from the earth's core. Of course, the third-order vital signs can't reach the core of the planet at all.

This is an underground vault that I had last roughly observed.

In the process of change, there will be dome bubbles as small as a few kilometers and as large as hundreds of kilometers, and even a cavity space connected by multiple bubbles, which is caused by rotation and fluid, and also has the influence of radioactive elements.

In fact, if Wu Dong wants to find the crystal, he does not need to go deep into the lower mantle layer, because the silicon element moves through the guò rock formation in the upper mantle layer, so that it is possible to create the most peculiar, stable and diverse crystal in the universe.

This crystal is an essential substance for the development of silicon-based life and carbon-based life to a higher level, and is an indispensable substance for the upgrading of the two organs of the heart core and soul matter.

The two guys, Mechanical War Dragon and Xiao Yi, who were tired of becoming dogs, dug an eighty-kilometer-long cave in five days, and they needed to go around the granite and pass through the softer basalt.

Wu Dong asked the two of them to make a hole diagonally diagonally - half a day later, the hole came out.

Thalia had never seen the underworld. In the modern scientific world, there is no such place at all, in the legend this is the world of magma and fire, which is comparable to the fire magic element that he cultivates, and what can be seen is not what the legend records.

The first is heat. There are about a few hundred degrees Celsius in the heat, and if the body of an ordinary person enters it, it has to be roasted into jerky or burned to ashes.

This underground space is about a few tens of kilometers away from the visual distance, and what supports it from collapsing is hundreds of huge rock pillars scattered everywhere.

The light was scattered by a flowing magma not far away, and the position of his group was a stone platform ten meters from the bottom level of the side wall of the space.

No one could breathe, let alone speak, because there was no air here.

All communicate in telepathic mode.

Xiao Yi is not a human being, Xiaoqin is a demon, and Xiaolan is not very intelligent. Only Talia and Wu Dong are human, and they have more urge to speak in words, while Natasha in the metal cabin is in a closed state. If there is no one, you can consider putting away the metal cabin, but you can't put it away if there are live animals.

The bottom is not all the same solid rock, and in some places it is extremely soft...... Fortunately, everyone is good, even if they stumble, they will not fall, everyone has changed into a metal skin, for the sake of beauty, everyone uses energy to show off some of their favorite "metal clothes" look.

Girls love beauty, Xiaoqin and Talia made two colors of gold armor in sky blue and gouache, and even made a pattern, which looks like a gold armor piece, and if there is a wind, it may still be able to blow.

Xiao Yi can transform into a human form, he reverted to the appearance of a little boy, made a set of ancient soldiers, and inserted a long sword in his back.

Xiaolan can't change the human form, but it doesn't like the original crab appearance, but changes into the appearance of the Oriental Divine Dragon, which is more than two meters long, and it is said that this look, it is a number of scans from hundreds of paintings, and the epidermis and body muscle cells have been reorganized, of course, the combat power, or the most powerful in the ontological state.

Xiaolan carried the metal cabin on his back, Xiao Yi opened the way, Talia walked in front of Wu Dong, Xiaoqin Finally, the group left the stone platform dozens of meters wide according to the way and route indicated by Wu Dong, and walked forward one foot deep and one foot shallow.

"Master, the life of the people in the underground is so hard, this place is worse than the ground!"

Wu Dong smiled, "You can't measure the living environment of the people on the surface to measure the creatures that may exist here, maybe for them, a temperature of more than 1,000 degrees is the normal body temperature." ”

Talia nodded, looked around, and found that the light was not very good, "Teacher, can you turn on the searchlight?" ”

Wu Dong thought about it, his perception of light can be adjusted, and he doesn't even need to use his eyes, but his partners haven't strengthened their eye organs yet.

"Okay. After a while to reach the magnet mountain sixteen kilometers ahead, I will build an anti-gravity thruster, so that everyone will not have to walk so hard. ”

Sixteen kilometers, walking for nearly an hour, bypassing two huge limestone subsidences, and jumping from time to time to finally reach the status of a magnetite mine.

A pure ferroalloy body about 1,000 meters high, black and red stone, with a temperature of about 1,500 degrees, is a very rare good material, and it is roughly estimated that there are tens of thousands of tons, which is more than enough to make an interplanetary vehicle.

However, they cannot be shipped out, they can only be manufactured in the extreme oxygen environment underground, or they can be made in space.

It was here that Wu Dong found obvious traces of excavation and cutting.

After turning less than three hundred meters around the Black Iron Mountain, a huge gap appeared in front of everyone.

"Someone has moved!"

Thalia exclaimed.

Wu Dong already knew, so he wouldn't be surprised, and Xiao Qin immediately took out his long sword and put him on guard, Xiao Yi realized it and took out a pistol.

The mechanical war dragon Xiaolan vigilantly turned on the range olfactory search.

Wu Dong observed carefully for ten minutes, and some information was searched.

"This is a sign that the underground mining truck has come, and it was here just a few days ago. It's supposed to be auto-mining - that is, if I'm not mistaken, we're supposed to have entered the territory of an unknown civilization, which is now being tracked and monitored. ”

"But, but I didn't find any monitoring equipment, master?" Xiao Yi asked puzzled.

Wu Dong's sense of perception had already swept what he was looking for.

"Go to the 6 o'clock direction, the rock a thousand meters away, there's a set of magnetic signal recognizers, destroy it."

"Yes."

Xiao Yifei shot out like a bird. When I got to the stone 1,000 meters away, I noticed an anomaly in magnetic sensation.

smashed the magnetic coil in a few clicks and returned to Wu Dong's side. (To be continued.) )