Lu Yuan raised his head and there was no red moon tonight.

Although the sun is extinguished, the gravity has not disappeared, and the earth is still rotating and autobiography under the constraints of gravity. Therefore, the time for seeing the sun is only about twelve hours in a day. Although the moon is also rising and falling in the east, under the influence of the earth's rotation, the time for seeing the moon is basically about twelve hours.

These are quite useful common sense in the solar calendar era, but at the moment when the sun is extinguished, you will only think of this when you cannot see the red moon.

But the stars are still brilliant.

Without clouds and atmosphere, the stars in the sky are dazzlingly lit and never flash.

Lu Yuan took another look at the pure starlight, took a breath in the heavy cold-proof mask, and then pressed the excavation button of the polar track truck.

At this time, they were above a ruined city, with ice and snow dozens of meters thick under their feet, but there were also many buildings exposed half on this desolate land.

However, most valuable items are buried, rather than in this extremely cold vacuum world. Polar track trucks have their own excavation system, part of which is used to dig out ice and snow to prepare oxygen. After all, although circulating oxygen is not feasible, when the foot is filled with oxygen, this cheap resource is really worth using.

Now, what Lu Yuan has to do is to carve a passage below the city so that he can safely reach the bottom of this snowy land.

When polar track cars are designed, they are mobile bases that can be self-sustained outside for a long time. Therefore, there is a sonar system specifically for this snow-covered city. You can follow the map to find the "treasure location" that suits you the most suitable for you.

At this moment, a cracking vibration came from below. The sound was harder than the snow, but it didn't look like a stone.

"What happened?" Lu Yuan asked Su Mei in the cold-proof clothing because Su Mei had a sonar surveillance.

"I don't know very well, it's a bit like a stone, but it's too brittle." Su Mei said: "But it's almost time to the hardened concrete floor, well, it's here."

Su Mei said: "You can go down and be careful."

Lu Yuan nodded. Now this is basically the best match between the two.

Although Lu Yuan is old, his body is still strong and powerful. His decades of shelter career have not seriously damaged Lu Yuan's health. Su Mei's current body is Lu Yao's sick body at the time. He basically has no way to walk outside. He can only huddle in the tracked car to do some simple surveillance and investigation work.

The two people complement each other, that is, Lu Yuan investigates and collects Su Mei stays at home.

Then communicate via radio.

At this time, in front of the distance, there is an ice and snow tunnel dug out by the polar track truck, which is about one meter in radius. It is slanted downwards and can slide down directly when you go down, just like a slide. When you come back, you either climb up with your ice boots and ice sleds, or the track truck will send it down and wrap it up with a rope and wrap it up.

Generally speaking, the latter will be chosen.

"Wish me good luck?" Lu Yuan said with a smile.

Even in this case, the two of them still often make jokes and support each other, although Su Mei often jokes that she does not have the talent for jokes like Lu Yao in the past.

"I wish you good luck." Su Mei said softly.

The road was long and jumped down.

The heavy cold-proof suit slid down in this one-meter-a-radius snow pit. Lu Yuan's hands were equipped with slowing ice skates on the backs of his hands, because the cold-proof suit is not absolutely solid and reliable, especially for such a slide that dozens of meters of the way. If there is a problem with the cold-proof suit under the acceleration of gravity, Lu Yuan will really finish playing on the spot.

This is also the first time Lu Yuan has observed the ice and snow covering the entire surface of the earth at close range.

When the sun is not extinguished and when pure oxygen and pure nitrogen are produced on the earth, the general industrial method is air separation. Through the principle of different melting boiling points between different gases, the air is liquefied by low-temperature boosting, and then gradually evaporates. Gas is obtained at each specific temperature, which is a relatively high-purity gas.

And after the sun goes out, the process turns around.

Because the earth's gravity is still there, the atmosphere still cannot escape from the earth. However, as the temperature on the earth's surface decreases, rain and snow will first drop. When the ocean, as the largest temperature buffer on the earth, all freezes, the speed of the earth's cooling will rush towards the distance.

In the history of this planet, there have been several glacial periods, and almost every glacial period means a mass extinction of species.

But never once did the earth become so cold.

The first thing condenses is water vapor. After the water vapor completely condenses, the air will become extremely dry and cold at the other extreme.

Among the common air components, the gas with the lowest boiling point is carbon dioxide, which condenses around minus 60 degrees Celsius. This usually-called greenhouse gas is also the most easily decomposed by cooling.

Therefore, the first snow and rain that humans saw were colorless rains formed by carbon dioxide.

Although the carbon dioxide component in the air is not high, there is no problem in such rain and snow for more than ten days or even months.

The cooling of the atmosphere is achieved through thermal radiation, and both the liquefaction and solidification of the gas must emit heat outward, which is also the final temperature balance of the earth after the sun is extinguished.

Because by burning fossil fuels, even if all fossil fuels are exhausted, it is difficult to compare to the solar energy that the sun pours onto the earth in one day.

After carbon dioxide, there are many kinds of rare gases. Most of the rare gases have higher melting boiling points than oxygen and nitrogen, so they will land on the ground one step ahead of time, and the earth will calm down for a while until the temperature drops to minus 200 degrees Celsius. The nitrogen, which occupies the highest component of the air, finally begins to liquefy and solidify slowly. This is a long tug-of-war. At the same time, with further cooling, oxygen will also be added. The snowflakes of oxygen are light blue. Because the melting point is close, they will mix with nitrogen and fall. In this process, the earth will gradually eliminate its atmosphere until it finally becomes a vacuum planet.

Therefore, the longest snowfall that humans have ever seen is this endless snow of nitrogen and oxygen that has lasted for decades.

As the temperature on the surface of the earth further decreases, this endless heat radiation will slowly stop, and the earth will slowly slide towards the extreme absolute zero, but it will never reach the end point.

This process may take tens of thousands or even tens of millions of years or hundreds of millions of years.

The road is far away in this distinctive ice and snow, and it seems to have witnessed the history of the earth for decades.

Then, Lu Yuan clicked and his ice skate caught something.

He turned around.

Under the lights of the cold-proof clothing, a human face looked at himself in a daze in the ice.
Chapter completed!