Why does the element we call "iron" (Fig.1) pop up everywhere? It supports modern architecture, carries us on long journeys, and controls our highly computerized society. It creates the Earth's magnetic field, makes photosynthesis work, and carries oxygen in the blood. Furthermore, it has been turned into weapons, agricultural equipment, and barbecue grills at the center of a happy circle. Is there anything or any phenomenon that doesn’t have something to do with iron?

Fig. 1──"Iron" in various languages, element symbol, and atomic number
I trust Google Translate.

On the other hand, there is no annoyance peculiar to things that pop up everywhere. Rather, iron is even modest. However, once we began to pay attention to it, we can see it everywhere. And we are all amazed at how iron cleverly does things and plays so many important roles. Sometimes as a leading character, sometimes as a supporting character.

Recently, the multiverse theory, which says that the universe we think of as the universe exists only when there are 10^1,000. to 10^10,000 universes with different properties, is being discussed not as science fiction but as cutting-edge physics. Jun Kosaka's "the Big Guide to Iron" is a picture scroll of the iron history of the universe in which we live. 13.8 billion years ago, just after the birth of the universe, a very small difference between particles and antiparticles resulted in a universe in which matter exists. The result was the birth of protons and neutrons, which we learn about in high school physics and chemistry, starting with hydrogen and helium. It was a monotonous world as far as the types of elements were concerned.

Innumerable elements such as carbon and nitrogen were produced inside the stars that were soon born. Then, when the red super giant stars and white dwarfs, which are the final stages of giant stars, underwent supernova explosions, heavy element—mainly iron—were born and scattered throughout space along with other elements. The solar system was created about 4.6 billion years ago in a corner of the galaxy based on hydrogen, helium, and these elements scattered throughout the universe. Currently, in the center of the sun, fusion reactions from hydrogen to helium takes place, producing a large amount of energy, but no carbon or iron. These were the wreckage of previously existing stars. That's why we are called "Children of the Stars." And iron is also a child of the stars.

During the time of social studies in elementary school, we learned that the area of the sea was 70% and the area of the land was 30% of the Earth’s surface, and it was firmly memorized in our minds that "the Earth is a planet of water." So, we are surprised to see Fig.2. Even if we add up all the water on the Earth's surface, including seawater, ice sheets, lake water, groundwater, and river water, there is only this much. On this scale, you can also feel how shallow the oceans are. According to the current knowledge of earth and planetary science, it may not be inevitable that the Earth has this amount of water. There was a possibility the Earth could have become a land planet with less water or an ocean planet with water everywhere you went. Rather, considering the amount of water contained in the meteorite that was the source of the Earth, it seems that it was no wonder that the seas were tens of times larger than the current ones [Fig.3].

Fig. 2──The Earth and all the water on it
https://water.usgs.gov/edu/gallery/watercyclekids/global-water-volume.html

Fig.3──Various types of planets: land, aqua, and ocean
https://speakerdeck.com/noinoi79528/nhk-karutiyajiang-zuo-huo-xing-ke-xue-zui-qian-xian-sheng-ming-wosu-suhuo-xing-falsetiao-jian?slide=29

Regardless of which of these—land, aqua, or ocean planets—the Earth could have been, iron would certainly have sunk to the center and become the core. However, the type of planet Earth became would have had a major impact on the fate of the iron on the planet's surface. As I introduced in my manuscript "Mirrored Japan -3: Archipelago without Iron," the main iron resources currently used are banded iron formations (BIF). The first important factor in its origin is that iron, which was present as a silicate mineral in rocks, dissolves in water to produce a rich iron soup. On land planets, where the amount of water is only 0.1% to 1% of that on Earth, such opportunities are very limited. Iron on land planets is still distributed in low concentrations in rocks. It cannot be called an iron resource.

At the other extreme, ocean planets whose surfaces are totally covered with seas, banded iron formations may form under various conditions. But who will use the iron that has accumulated at the bottom of the deep sea? There is also no place to build a steel mill. In the first place, the BIF will be buried in the sediments of the deep sea, and its existence will not be noticed. The BIF will be a hidden treasure unless sedimentary rocks in the ocean become part of the continent through tectonic movement in the aqua planets.

For some reason, the Earth chose a career as an aqua planet. Even so, it was so lucky that the sun is an unnoticeable star and mundane in size in the galaxy. The larger the size, the faster the fusion reaction progresses, and the shorter its life. The lifespan of a giant star, which weighs ten times as much as our sun, is said to be less than 100 million years. Since the main energy source for orbiting planets is the light received from the stars, it would be a problem if the essential stars were to disappear in a blink of an eye. We do not have long enough to conduct an experiment on biological evolution. There is not enough time for you to roll the dice enough times. “Role of Iron in Life: A Review" by Wataru Takahagi and Norio Kitadai is an ambitious work that discusses how iron has played an important role in the evolution of life on the aqua planet Earth, which has been given more than four billion years to evolve. This paper shows that the key factors for the selection of iron for life are the abundance of iron, the fact that Fe²⁺ and Fe³⁺ have almost the same complex structure in proteins, and the characteristic of making bonds of moderate strength to both sulfur and oxygen. And these first two characteristics are just the main factors that led to the selection of iron as the key element for hemoglobin in the blood.

We cannot artificially create hemoglobin from scratch. However, it is becoming possible to reprocess blood that is donated but happens to be discarded without the opportunity to use it. Hiromi Sakai's "Iron-Dependent Oxygen Transport by Red Blood Cells and Artificial Red Blood Cells" explains in detail the role of hemoglobin in blood and derives a solution to the chronic shortage of red blood cell preparations for blood transfusion. The importance of artificial red blood cell development is undisputed in preparation for the large demand and rapid supply of blood for transfusion in the event of a large-scale natural disaster, terrorism, or other emergency. As a pioneer of this technology, Sakai has put together many studies and is leading a research team with the aim of putting artificial red blood cells into practical use and popularizing them.

By the way, when did we human beings consciously start to come into contact with iron? Life was connected because iron, which is an essential element, happened to be contained in the foods we put in our mouths when we felt hungry. Thus, for most of the 200,000-year history of Homo sapiens, we were free of iron deficiencies. It is only recently that we have become more conscious of food and iron, daring to eat iron-rich foods and taking iron supplements.

Mural paintings may be the first archaeological evidence to record the conscious encounter between Homo sapiens and iron. The stunning yellows and reds of hydrous iron oxides fascinated people and became an indispensable state-of-the-art paint for ancient artists. It is excellent not only in color development but also in preservation, and many works remain such as innumerable cave paintings [Fig. 4]. People may have painted their faces and bodies during rituals and fiestas. Moreover, not only these clay-like iron oxides, but also iron ore, which is clearly heavier than other stones, must have been a point of focus for ancient people who were sharpened in the five senses. Iron ores of unknown use have also been described from the Tenjinbara site of the Jomon period in Gunma Prefecture, Japan.

Fig.4──Examples of mural painting using hydrous iron oxide
Claude Valette, CC BY-SA 4.0 , via Wikimedia Commons
By Museo de Altamira y D. Rodríguez, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24512679

It's quite amusing to imagine life on a land planet★1 [Fig.3]. There are no oceans there, only small seas, so the banded iron formations would never have formed. Would the iron resources have formed so-called bog iron as seen in Northern Europe? There are also very few wetlands, so there would be very little coal. Limestone would have been also extremely valuable, as there would have been no corals and no calcareous planktons. Then, even if human beings lived for many years, the Industrial Revolution would have been unlikely to occur. Of course, if the seas were limited, there are few places in which oil would originate. The internal combustion engine would not have been invented, and there would be no plastic. There's nothing there. It is becoming clear that the hunting and harvesting life was richer, with shorter working hours and offering a better nutritional balance than it is today. If humankind was created on a land planet, such a life might have continued forever.

When we wake up from delusions and look at reality, we live on the Earth, where the area of the sea occupies as much as 70% of the planet. Was it the naturally occurring metal sulfide or the iron meteorite that first grabbed people's attention with its mysterious metallic luster? It seems that our ancestors, who lived on an aqua planet, were not satisfied with the artistic activities of iron that remained bound to oxygen. It was in Anatolia around 2300 BC that metallic iron, in which iron does not combine with oxygen, appeared in human activities. The iron dagger excavated from the tomb at the Alacahöyük site was a processed iron meteorite. The first metallic iron we used was one that had fallen from space and was in the state of metallic iron from the beginning. Did the ancient alchemists of the era—a time when the concepts of elements, compounds, oxidation, reduction, were not yet defined—try to make the same thing by referring to the metallic iron that had fallen from space as a model? In an interview article "Anatolia and the Origins of the Relationship between Iron and Civilization," Sachihiro Omura talked about the beginning of how people interact with iron. Omura was a kids' archaeologist in Iwate, where is the same birthplace as Los Angeles Angels' Shohei Ohtani, but he decided to take a leap of faith and has been excavating a single site in Anatolia for more than 30 years (the time of writing is August 19, 2021, but in fact he is still directing the excavation at the Kaman-Kalehöyük site in order to regain the time lost in 2020 due the Corona pandemic). He and his team are honestly and painstakingly excavating the site and following the mind-boggling policy of describing and preserving all excavated items. A high school history textbook states that the Hittite Empire developed the first steelmaking technology, concealed it, and maintained its technical significance. However, many years of excavation by the team led by Omura have found metallic iron, which is not an iron meteorite, in strata older than the Hittite Empire. Here too, common sense is changing.

At the final stage of the interview, Omura said that the beginnings of steelmaking in Anatolia and the Industrial Revolution of the 18th century are connected, and Norihito Nakatani's "Steel and the Origin of Building Mode 3" elaborates on the relationship between people and iron during and after the Industrial Revolution. And sure enough, the Industrial Revolution took place on an aqua planet, which is rich in iron ore, coal, and limestone. Although Nakatani is not a geologist, he found that the raw materials that triggered these Industrial Revolutions were distributed in close proximity in Europe and North America, and that the Caledonian orogeny was related with characteristic distribution. I am not sure if there are any other researchers in architectural history who focus on the Caledonian orogeny. Mankind who was able to convert iron ore into steel, and with this mass-producible, flexible, and strong material in our hands, we have turned our activities to the sky.

Noriko Matsuda ed. "Graphics: Steel and the Origin of Building Mode 3" is paired with Norihito Nakatani's "Building Style of Steel." Here you can see what kind of sights were engraved on the surface of the Earth as we continue to make a large amount of steel, and what we have created with that steel. With steel—the magical material—we were able to expand our imaginary wings to infinity. The way we use our land has changed, allowing us to even take off from it.

Nearly three centuries have passed since the Industrial Revolution, and advances in science and technology are accelerating. When we look around, there is iron beside us even now. It's still the Iron Age★2. One consequence of this Iron Age would be the various weapons that enable mass slaughter. Tanks, shells, giant battleships, and aircraft carriers. Countless war-dead ships, which are huge chunks of steel, are sunk in the world's oceans. Decades later, these steel masses are densely covered with a myriad of sea creatures★3. In contrast, lighter duralumin military aircraft have fewer organisms attached to them. The attraction is unique to iron. Of course, the phenomenon is not limited to military ships. The Titanic, which sank into the cold deep sea in an accident, has become a paradise for iron-oxidizing bacteria★4. At this point, the iron cycle was finally connected. Banded iron formation created by the photosynthesis of cyanobacteria over 2 billion years ago. A huge mass of steel produced, as one of the goals of human activities, from BIF returns to the world of living things [Fig.5].

Fig. 5──Coral-covered wreck
Wiki.mjmasangkay, CC BY-SA 4.0 , via Wikimedia Commons

Having confirmed the iron cycle, I was satisfied and felt as if I had settled this issue, but Naganuma did not stop there. In another interview article with Takeshi Naganuma's "Iron, Life, and Metabiosphere" he was looking at space with a serious look. His concept of "Metabiosphere" comprehensively captures not only the Earth but also the Moon and Mars. I thought that the ideas of moving to space was expedient to get a budget, but history doesn't go forward with just such people with low vitality. There is a person having ambition here. Naganuma is famous as a hunter of microorganisms living in extreme environments, but during the interview, I was staring at him with an intense look at a mysterious organism.

If "Iron is always there," we can think of countless things and phenomena that can be considered. Of course, this special issue has not covered all the important themes related to iron. Here, we chose to compose this special issue from the perspective of the significance of iron's existence on the Earth, the history of the relationship between humans and iron, and the future relationship, which is occurring based on the relationship between iron and living things. This is a story of iron set in the "aqua planet where the area of the oceans consisting of liquid water occupies 70%" that orbits the "star of mediocre size that lasts 10 billion years" in a "universe where iron exists." In this "How to read HBH web No.3," I gave priority to telling the planning intention of the special feature as a series of stories, so I could not touch on many of the important points of each work. I hope that you will enjoy this special issue with your interests.

★1──Conversely, an imaginary life on an ocean planet is depicted in the movie "Waterworld."
★2──Vaclav Smil (2016) Still the Iron Age: Iron and Steel in the Modern World, Butterworth-Heinemann.
★3──http://www.tanaka-masafumi.net
★4──http://www.bbc.com/earth/story/20170310-the-wreck-of-the-titanic-is-being-eaten-and-may-soon-vanish

Takashi Ito
Geology, Ore Geology, Earth Science Education
Professor of Education at Ibaraki University