The air changed at the boundary of the Shield. Outside it was dry and thin. Inside there was density. Yujin stood before the boundary and pulled off her glove. The fingertips of her left hand were a black-violet. From beneath the nails to the first knuckle. It was the mark of magnetic material deposited under the skin. It had seeped in over 3 years working on the Shield construction site. The medics had said it couldn't be removed. They said the magnetic material had bonded with the capillary walls, and separating it would rupture the vessels. Yujin flexed her fingers and straightened them. Sensation was normal. Strength was normal too. The medics told her to get examined every 6 months. They said it would become a problem if the deposit spread to her heart. For now it reached only her fingers and the back of her hand. Yujin lowered her hand and put the glove back on. It was only that near a strong magnetic field her fingertips prickled. And when the pressure shifted before rain, the joints of her fingers throbbed. The magnetic material expanded minutely with the change in pressure. The boundary of the Shield was that kind of place.
Yujin cinched the straps of her backpack. Inside were 2 water filters, 7 days of compressed rations, 1 medical kit, and 1 spare UV-shielding suit. At her waist she wore a magnetometer and a transceiver. The meter was one she'd used at the Shield construction site—a device that measured Ferrocell particle density and magnetic field strength in real time. 380 grams. Palm-sized. She'd carried it every day on the site. The transceiver's effective range was 40 kilometers from the Shield's boundary. Beyond that, the electromagnetic interference of the solar wind made communication impossible. Gaeun, the village where her younger sister Yura was, lay 52 kilometers past the boundary. It had been 18 days since the last transmission cut out. There was no way to confirm whether she was still alive. For the Shield expansion works to reach Gaeun would take 4 months at the very least.
Behind Yujin lay Incheon, the city inside the Shield. Population 3.4 million. The Shield covered the city in a hemisphere—28 kilometers in diameter, 12 kilometers high. Its material was a synthetic magnetic substance called Ferrocell: nanoscale magnetic particles dispersed through a gel matrix, forming an artificial magnetic field that deflected the charged particles of the solar wind. In the days when Earth's own magnetic field still held, nothing like it had been necessary. Eight years ago, the strength of the planet's magnetic dipole had fallen below the critical threshold. The solar wind began striking the atmosphere directly. The ozone layer thinned by 40 percent in three years. The UV index sat permanently at the extreme-danger level. Outside the Shield, skin burned in 15 minutes. The eyes went faster—look at direct sunlight without protection and the cornea was damaged within 10. Outdoor activity was confined to dawn and dusk. In the full light of day, you had to stay underground or inside a shielded structure.
Yujin passed through the Shield. The moment she crossed the boundary layer, her left hand went hot. The magnetic material beneath her skin was reacting to the Shield's field. The flux density was highest right at the boundary. The heat spread from her fingertips up to her elbow. 3 seconds. Once she cleared the boundary, the heat was gone. Yujin looked at her left hand. The blackish purple seemed a shade deeper. There was no way to be sure. The spread of the deposit was a slow process. It didn't change enough to see with the naked eye in the span of a day. But she knew that every pass through the Shield accelerated it. Yujin pulled up the hood of her UV suit and put on her goggles. The suit was nylon with a silver reflective coating. It covered her whole body except for her face and hands. She pulled her gloves back on.
Outside, it was quiet. A wind was blowing. A dry wind. The sky was different from usual. Inside the Shield, the sky was blue. The sky outside was a pale purple. As the oxygen concentration in the atmosphere dropped, the scattering wavelength had shifted. Yujin checked the UV filter on her goggles and looked east. She could see the road. Dust had piled up on the asphalt. Traffic had stopped long ago. She walked along the road. Dust rose beneath her feet. It smelled of dry earth. Here and there along the roadside stood abandoned vehicles. Their tires had cracked apart. The rubber had broken down under the ultraviolet light. The plastic of the door handles had crumbled to powder and fallen to the ground. Only the metal parts held their shape. They were red with rust.
Two hours later, Yujin reached the first derelict building. A gas station. The roof had caved in. UV degradation of the materials—plastic and rubber broke down first. The support strut of the station's canopy had snapped. Yujin drank water in the shade. It tasted metallic. It had passed through the purification filter, but it was nothing like the tap water inside the Shield. Sweat ran down her back. The shield suit was trapping the heat. She cracked the hood open a little, letting air onto the nape of her neck. She checked the magnetometer. 14 kilometers past the Shield's boundary. Magnetic flux density 0.003 gauss. About a hundredth of the Earth's magnetic field. She checked the radio. Signal strength, 2 bars. Yujin switched it on. "Control, this is Yujin. Past the boundary, 14 kilometers. Nothing to report." A reply came back laced with static. "Yujin, Control. Copy. Request final check-in at the 40-kilometer mark." Yujin switched the radio off.
The sun began to sink. Yujin walked. Farmland stretched away on both sides of the road. There were no crops. The soil was cracked. Ultraviolet radiation had killed the soil microbes. Soil without microbes could not sustain crops. Here and there a dead tree stood. There were no leaves. The bark was split. Yujin touched the bark of a tree. It was dry. It crumbled. Powder ran down between her fingers. When the tree had been alive, this road would have had shade. Yujin leaned against the trunk and rested a moment. The trunk gave a dry rustle. It could have snapped at any time and no one would have wondered.
At the 40-kilometer mark she made her final check-in. The signal on the radio had dropped to 1 bar.
"Control, this is Yujin. Past the 40-kilometer mark. Expect no further contact from here. Will re-establish contact upon return, after reaching Gaeun village."
The reply cut out, then came back.
"Yujin, copy. If no contact within 72 hours, we send a search team. Be careful."
The line went dead. Only static remained. Yujin put the radio into her pack. From here on she was alone. 40 kilometers behind her lay the Shield, 12 kilometers ahead lay Gaeun village. She could reach neither.
She walked another 12 kilometers. The sun was setting. The afterglow was a red-violet. It was a color you could never see inside the Shield. It was too dangerous a sky to feel was beautiful. Yujin decided to spend the night in a concrete building beside the road. It was a building with no windows. The concrete walls were 40 centimeters thick. The walls were thick. They could hold off the ultraviolet and the nighttime drop in temperature. Yujin went inside and spread her mat on the floor. She took out a compressed ration bar and ate. It was hard. It took effort to chew. She drank a mouthful of water. She looked at her left hand. When she pulled off the glove, she could see the black-violet in her fingers. During the day the gloves of the shield suit hid it. At night it came out. Yujin pressed the tip of her index finger. There was no pain. The skin's elasticity was normal too. Only the color was different. It showed even in the dark. Beneath the skin came a faint light. The magnetic material was reacting to the residual magnetic field and fluorescing. Yujin closed her hand and opened it. The glow flickered. It was the rhythm of a heartbeat.
She set out at 4 in the morning. The hours before sunrise were when the ultraviolet was weakest. Yujin walked for 3 hours. Gaeun village began to come into view. A structure stood at the entrance to the village. Yujin stopped. It was something she had not expected.
The structure was an arch 5 meters high. Metal and earth and plant stems were woven together. Silver reflective material covered the top of the arch. A material like the shield suit. But it was not an industrial product. It was aluminum cans flattened and joined together. Hundreds of cans overlapped to form a reflecting surface. Passing beneath the structure, you could escape direct sunlight. Yujin stepped in under it. The shade was cool. She felt the temperature inside her shield suit fall by about 2 degrees. The structure of the arch was not simple. Below the reflective material was a layer of air. A double structure, insulating and reflecting at the same time. Clay had been smeared on the inner face of the arch. Small stones were set into the clay. At regular intervals. Yujin touched one of the stones. The magnetometer responded. It was a magnetic stone. Magnetite. A natural magnetic mineral. Someone had arranged magnetite at regular intervals to make a weak magnetic field.
As she entered the village there were more structures. Reflective canopies bridging one building to the next. The mouths of passages leading underground. Clay layers with magnetite set into the walls. The whole village had been transformed into a structure for blocking ultraviolet and reinforcing the magnetic field. It was not industrial technology. It was made from scavenged materials and natural minerals.
A sound came from an alley. Yujin turned. A child stood there. It looked about ten years old. White paint was smeared on its face. Zinc oxide. Ultraviolet protection. The child looked at Yujin's shield suit. It looked at Yujin's face. It turned and ran. It was barefoot. The soles of its feet were cracked, but its running was fast. Yujin followed the child. The walls of the alley too were smeared with magnetite clay. The whole village was a single shielding structure, loose but connected.
The place the child led her to was an underground space at the center of the village. Somewhere that had once been an underground parking garage. Ventilation shafts had been cut into the ceiling. Inside there were people. Close to 20. Mats and blankets were spread on the floor. Along one wall water bottles stood in a row. On the opposite wall tools hung. Shovels, pickaxes, scissors, knives. All of them metal. Not one plastic tool. Yujin stood at the entrance. The people looked at her.
"You come from the Shield?"
said the person standing at the front. Lean of build, the backs of the hands cracked. Yujin nodded.
"Where is Yura?"
There was a movement among the people. Yura came out. Yujin's younger sister. Zinc oxide was smeared on her face. Her skin was burned dark, but she looked healthy.
"Sis."
said Yura. Her voice was cracked. Yujin held Yura. Yura's body was thin and hard. Bone met her hands. But the muscle was alive. It was the body of someone who dug earth every day, drew water, plastered walls.
Yujin opened her backpack and took out a medical kit and a water filter.
"I can get you inside the Shield. Incheon is 52 kilometers. Two days and we're there."
Yujin said. Yura looked at her. Yura's eyes came to rest on Yujin's left hand. The dark purple of the fingertips, showing above the glove.
"Sis, what's that on your hand?"
"Ferrocell deposits. From the construction sites."
Yura shook her head.
"Not that. I know it's safe inside the Shield. But the people here won't go."
Yujin looked at her.
"Why?"
"Because we can live here. For 2 years we built a way to live here. The people here made it. Why would we throw all this away and go into the Shield? To move into a refugee camp? There isn't even enough room inside the Shield."
Yujin couldn't answer. It was true. Incheon's population density had tripled since the Shield went up. There wasn't enough housing. There were plans to take in the people from the outer regions, but the space actually assigned was cramped and squalid.
Yura walked Yujin through the village. There was an underground farm, built on the second level of an underground parking garage. Light came down through the ceiling vents. The light had passed through an ultraviolet filter, a filter made of glass bottles filled with water. The water absorbed part of the ultraviolet. Beneath the filter, vegetables were growing. Lettuce, radish, cabbage. The leaves were small but vivid in color. Yujin picked a lettuce leaf and looked at it. It was fresh. The leaf was thicker than the ones they sold in the markets inside the Shield. The soil was earth brought from outside the village, mixed with compost. It was living soil, full of microbes.
"The soil outside is dead."
Yujin said. Yura answered.
"We brought it back. We made compost and cultured the microbes. It took 2 years."
Yura showed her the water system too. A hand pump drawing up groundwater. A filter made of sand, charcoal, and gravel. A three-stage filtration structure. The reservoir was a pit of concrete walls sealed with waterproof clay. All of it built without a single industrial product.
"And the comms going down?"
Yujin asked.
"There was a week when the solar wind was strong. All the electronics burned out. The transceiver too."
Yura said.
"But you survived."
Yura looked at her.
"Because we were underground. The magnetite walls blocked some of it. Not as much as an industrial Shield. We learned how to live here."
That night Yujin slept in the underground space with the others. Through the ceiling vents she could see the night sky. The stars were sharp. The Milky Way was there. Inside the Shield, the magnetic field deflected the charged particles in the air, and that bred a faint distortion of light. The stars were blurred, and the Milky Way couldn't be seen. The last time Yujin had seen this sky was 8 years ago, before the Shield was built. She raised her left hand and looked at it under the starlight. The fluorescence at her fingertips glowed faintly. Yura, lying beside her, took her hand.
"There's light coming off your hand."
"It's magnetic material. It reacts to magnetic fields."
"Does it hurt?"
"No. The feeling's normal."
The next morning, Yujin joined the villagers repairing the magnetite wall. The work was kneading clay, laying out pieces of magnetite, and spreading it over the face of the wall. Yujin took a magnetometer from her backpack and checked the arrangement of the magnetite. Numbers came up on the meter's screen. The arrangement wasn't even. The spacing was irregular. Yujin raised the meter and scanned the wall.
"If you narrow the spacing here to 3 centimeters, the field density goes up almost double."
Yujin said. One of the workers looked at her.
"How do you know that?"
"I was a Shield construction engineer. Magnetic material arrays are my specialty."
The others made room for her. Yujin knelt down in front of the wall. Watching the meter, she adjusted the spacing and orientation of the magnetite. Rearranging a single wall took 2 hours. When she was done, she checked the meter. The field density had risen from 0.008 gauss to 0.014 gauss. Still weak, but better than before. Enough that on a day of strong solar wind, they could hold out inside this wall for about 30 minutes without fleeing underground. Yujin checked the result and stood up. Clay was smeared on her knees.
At lunch Yura asked her.
"How long before the Shield expansion reaches this far?"
"Four months."
Yura nodded.
"Four months, we can hold out here."
"I can teach you the magnetometer I brought and the array technique. Raise the efficiency of the magnetite walls and you'll be able to hold out underground even on days of strong solar wind."
Yura looked at her.
"And in return, there's something we can teach you."
"What?"
"How to bring this soil back to life. The soil inside the Shield is dying too, isn't it?"
Yujin looked at her. It was true. The Shield had stopped the solar wind, but the Shield's magnetic field was affecting the ecology of the soil microbes. Harvests from the farmland inside the Shield were shrinking every year. The Shield construction team had never accounted for what the magnetic field did to the soil. Yujin herself had spent 3 years building the Shield without knowing about the problem.
Yujin stayed 3 days in Gaeun village. The first day she optimized the arrangement of the magnetite walls. She measured the magnetic field density at 7 of the village's main structures, adjusted the arrangement, and recorded the results. She handed the records to the villagers. The optimal spacing, orientation, and layer thickness of the magnetite. She converted it all into finger-widths so it could be applied even without a meter. The second day she learned composting and microbe cultivation from Yura. The list of materials, the temperature conditions, the cultivation period, the ratio and timing for working it into the soil. Yujin wrote it all in her notebook. How to check the compost's temperature by hand. When the microbes activate, the inside of the compost climbs to 60 degrees. If you can't hold your hand in it for 5 seconds, it's the right temperature. A technique for judging by sense, without industrial equipment. The third day she gave Yura the magnetic-field meter.
"This is the one I've been using."
Yura said.
"Is that okay?"
"There are more meters inside the Shield. This is the only one out here."
Yura took the meter. She switched on its screen. The magnetic field density appeared on the display. Yura held it up to the wall. The number changed. The corner of Yura's mouth lifted.
The morning she left, Yujin shouldered her backpack. It had grown lighter. She had left half her medical kit, water filter, and compressed rations behind in the village. The meter was gone too. Yujin's left hand prickled in front of the magnetite arch at the village entrance. The magnetic material in her fingertips was reacting to the arch's magnetic field. Yura stood before her.
"When the Shield comes, 4 months from now."
Yura said.
"I'll be here until then."
Yujin nodded. She held Yura. The smell of earth rose from Yura's shoulder. The smell of living soil. A smell you couldn't catch inside the Shield.
Yujin walked. 52 kilometers. She was retracing the road she had come by. Dust lifted from under her feet on the road. The sun was climbing. Light spread above the horizon. The purple sky brightened. Yujin lowered her goggles and cinched the hood of her shield-suit. The suit's reflective coating threw back the light. Inside the glove on her left hand, her fingertips trembled faintly. When she crossed the boundary on the way back, the heat would come again. The magnetic material would spread a little further. Yujin did not stop walking. The prickling in her left hand grew stronger with every step. She was getting closer to the Shield. Even from far off, the boundary's magnetic field was working on the magnetic material in her fingertips. 20 kilometers. 10 kilometers. The prickling turned to a throbbing. In her backpack was the compost method Yura had written out for her. The notebook's pages rustled inside the pack. Yura's handwriting was in there. Yujin clenched her left hand and opened it. The glow at her fingertips was invisible in broad daylight. But it was there. Yujin knew it. The boundary began to come into view. The point where the air changed. The line between the dense air inside and the thin air outside. Without slowing, Yujin walked into the boundary. Her left hand went hot. The heat climbed past her elbow to her shoulder. The range was wider than before. Yujin clenched her teeth and walked. 5 seconds. She passed through the boundary. The heat vanished. The air inside the Shield filled her lungs. Yujin stopped, caught her breath, and pulled off her left glove. A black-purple had spread from her fingers to the back of her hand. Before she left, it had only reached her fingertips. Yujin pulled the glove back on. The sensation in the back of her hand had dulled. Whether the nerves had begun to go, or it was only the pressure of the glove, she couldn't tell. Yujin clenched her hand and opened it. The fist closed. It still moved. Inside the backpack, the notebook rustled.
