With nearly 500 milliliters of Evolution Agent, Lin Feng returned to the camp to initiate his final minor level evolution before advancing to Tier Two.

After completing the Level 19 evolution, it signified that the Tier One cells within him had reached the stage's upper limit, with only an accumulation of quantitative change afterward and no qualitative breakthroughs.

Inside the Rock Horse Battle Car, Lin Feng observed the Leader Level Rock-Horned Horse Life Source Material in his left hand and the Level 17 filter in his right, falling into contemplation.

Currently, the maximum aperture of the Source Material Filter had narrowed down to 20 nanometers. If it were to rise by just one more level, it could achieve the degree of filtering Tier Two Source Material!

At that time, conditions for filtering Tier Three Source Material should also appear. If successful, it would imply that Lin Feng's evolutionary resources for the next few years could rely on the secondary processing of the Source Material Filter.

After purifying and filtering the Level 19 Rock-Horned Horse Source Material in hand, obtaining a full cup of Pure Source Material, Lin Feng first expended five Life Value points to continue upgrading the filter.

Then, after consuming a piece of dried meat to recover Life Value, he also provided ample energy for the upcoming evolution.

A large cup of pure life source material was slowly consumed, and the substantial source material began to drive the evolutionary cells within to deeply optimize and transform.

Gradually enhancing the strength and life force of cells.

Half an hour later, Lin Feng slowly awoke from the bed, opening his eyes to see the evolution completion reminder:

"Lin Feng, lv19/19"

"Life Value: 150, Physique: 150, Spirit: 149; lv19 attribute upper limit 150"

"Superpower Awakening: Power of Branding (slightly increases Branded Equipment upgrade speed)"

"Item upgrade limit raised to lv19!"

"Five Life Value points available to continue upgrading lv18 Machine Cannon Gun, lv18 Rapid Fire Cannon, lv18 Source Material Filter"

Lin Feng narrowed his eyes slightly, then checked the Level 18 Source Material Filter that had been upgraded beside him:

"Nanometer-Level Source Material Filter lv18, Red Quality, Brand"

"Basic Attributes: Maximum aperture 10 nanometers, Tier One gene impurity filtering degree: 100%; Tier Two impurity filtering degree 100%; Usable times 1; Five Life Value points can be consumed for an upgrade"

"Evaluation: Capable of perfectly filtering alien gene impurities from Tier One and Tier Two Life Source Material, obtaining pure source material to achieve Purity Evolution; Tier Three Life Source Material filtering degree limited, requiring maximum aperture equal to 1 nanometer to achieve complete impurity filtering"

Although attaining the anticipated effect, Lin Feng was not very happy because the Tier Three Source Material degree actually required less than one nanometer!

This suggests that its aperture had reached the atomic level.

Lin Feng recalled learning about chemistry long ago, which introduced atoms as the most basic units that make up matter, sized between below one nanometer to picometers.

One millimeter equals one thousand micrometers, this scale represents the size of single cells and bacteria.

One micrometer equals one thousand nanometers, this scale measures chromosomes, viruses, and some large molecule proteins, etc.

And one nanometer equals a thousand picometers, a scale that measures the size between atoms.

The specific size depends on the mass of the atomic nucleus, more accurately, the number of protons carrying a positive charge, determining the number of electrons of the atom, thus affecting the size of atoms.

Like the small hydrogen atom, it's approximately 0.1 nanometers, which is one hundred picometers, while other massive atoms are around a few hundred picometers.

Therefore, an aperture less than or equal to one nanometer can absolutely screen all impurities.

Of course, some small molecular substances can pass through, but ribonucleic acid containing genetic information will surely be blocked outside, ensuring that the filtered life source material is absolutely pure.

However, Lin Feng was also concerned about this point.

Originally, he thought the aperture that could filter Tier Three Source Material would at most be under ten nanometers, and that upgrading to Level 19 should be sufficient.

Seeing now, it requires less than one nanometer to be secure, thus the Level 19 filter could not satisfy this, needing at least to match Tier Two Orange Quality equipment to achieve complete impurity filtering.

Thus, before advancing to Tier Two, unless using the branded forced upgrade skill to consume the cost of dropping one evolution level, forcibly advancing, otherwise the filtering of Tier Three Source Material seemed distant.

He hoped Bai Ye would keep the promise.

After clearing the negative third layer, hand over that Clan Leader Level Rock-Horned Horse Tier Two Source Material to him.

Otherwise, Lin Feng would not agree to accompany them below the negative third layer.

According to what they said before, the military factory is likely located in the bottom three lower layers beyond the negative sixth floor, filled with various dangerous pollution sources.

Moreover, once pollution sources are enriched, they would give birth to a Tier Three Mutant King.

As the Salvation Army opened the sealed gate, no one knew if only one Tier Three Mutant ran to the middle and upper layers of the ruins.

By then, without the strength of Tier Two evolution, Lin Feng would surely escape with the Church Squad first.

Having made plans for afterward, Lin Feng, while eating Evolutionary Dried Meat, performed the last upgrade before Tier Two for the Rapid Fire Cannon and Armor-Piercing Cannon.

Soon, according to the predetermined upgrade and reinforcement strategy, both heavy firepower weapons were fully upgraded:

"Rapid Fire Cannon lv19, Red Quality, Brand"

"Basic Attributes: Damage 120, Effective Range 2 kilometers, Damage Coverage 8 meters, Remaining Explosive Shells 4000; Upgraded to Host Level Limit"

"Extra Attributes: Ammo Recovery 1/1s; Space Magazine 4000 rounds; Area Damage (Coverage Radius 8 meters, Center 1 meter Damage 120); Rapid Pursuit (Automatic Mode 10 rounds per second)"

"Note: Can freely switch back to lv9 High-quality AK"

After leveling up to the second stage full level, the Rapid Fire Cannon possessed a total of four thousand ammunition reserves, and the entire gun body gradually transformed from the previous high-quality AK model into a current heavy machine gun state exceeding one and a half meters in length.

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