SECTION THREE: THREATS FROM EARTH
From space, our Earth stands out as a beautiful blue planet that is completely unique. It is the only ecological planet and the only civilized planet within humans’ current field of space vision. Its beauty is unparalleled.
The earth is mainly composed of metals and rocks, and its surface is mainly ocean. Earth is more than 70 percent composed of ocean, while land occupies less than 30 percent of the earth’s surface. Earth is not perfectly spherical in shape; its equatorial radius is about 6,378 kilometers, twenty-one kilometers larger than its radius. Earth’s highest peak is Mount Everest, measuring 8844.43 meters in altitude, and its deepest ocean is the eleven-kilometer deep Mariana Trench. Overall, the total surface undulation of Earth is twenty kilometers.
The earth’s interior is made up of the core, mantle, and crust, while the exterior is composed of the hydrosphere, atmosphere, and magnetic field. The different parts of Earth’s interior and exterior form the whole of Earth.
Earth is the mother of humans; it gave birth to and continues to nurture humanity. But the Earth is not a gentle mother—earthquakes, volcanoes, floods, and storms have claimed the lives of and brought suffering to count-less people and made many others homeless. We have profound understanding of Earth’s importance to humanity, and we are uniquely attached to it. Without Earth, humans would not be able to survive, which is why we must consider how Earth may influence human survival.
One: Plate Motions, Earthquakes, and Volcanoes
As early as the nineteenth century, while laying cables on the ocean floor, people discovered that the central seabed of the Atlantic was shallower than its edges. After further study of the Atlantic, a central ridge was discovered rising from the depths of the ocean. Islands like the Azores and Ascension are all the exposed parts of that ridge. While conducting echo detection in the Pacific Ocean afterwards, scientists found a long, flat-top seamount along the eastern Pacific seabed as well.
In the 1950s, research of the ocean became more thorough, and scientists confirmed that a continuous sixty to seventy thousand-kilometer-long submarine mountain range existed in the world’s major oceans. Since this mountain range was located in the center areas of the Atlantic and Indian oceans, it was named the mid-ocean ridge. The aforementioned Atlantic central ridge and Pacific flat-top seamount are both parts of the mid-ocean ridge. The total length of the mid-ocean ridge is enough to circle Earth twice; none of Earth’s land mountains can compare with this unseen mountain buried deep under the sea.
Further study of the mid-ocean ridge showed that a deep rift existed on top of the ridge, one thousand to two thousand meters in depth. It splits the mid-ocean ridge in two, a phenomenon that is particularly evident in the mid-Atlantic ridge. Frequent earthquake and volcano activity can be found near the mid-ocean ridge. Through seismic wave analysis, it is possible to determine that the seismic wave velocity at the mantle of the mid-ocean ridge is smaller than it is at other mantles, showing that the mantle material underneath the mid-ocean ridge is hotter and lighter. The continuous expansion of this material caused the mid-ocean ridge to rise up.
Further understanding of the ocean also includes oceanic trench detection; the deepest sea trench is two thousand meters higher than the world’s highest peak. Among the world’s oceans, the Pacific coast has the most wide-spread distribution of trenches, as well as the most significant drops.
After summing up large amounts of geological surveys and research data, scientists proposed the theory of seafloor spreading. They believe the upwelling of Earth’s mantle to be the driving force of the ocean’s expansion. The top of the mid-ocean ridge is like an outlet for the rising magma, which tears apart the oceanic crust and pushes it to the side. Once the magma cools it fills the tear, causing the mid-ocean ridge to expand on both sides. The uplifting of the mid-ocean ridge is the result of thermal expansion from rising magma.
To be specific, it is rising magma from the mantle that expands the mid-Atlantic ridge and splits the Atlantic Ocean into the West Atlantic and America side, and the East Atlantic, Africa, and Europe side. Continuously rising magma constantly pushes the oceanic crust of both sides, moving the western Atlantic Ocean and America further westward, and the eastern Atlantic Ocean, Africa, and Europe further eastward. That is why the Atlantic is becoming wider and wider.
Where does the space from the mid-ocean ridge’s expansion come from? In other words, as the Atlantic is widening, which area is shrinking accordingly? The answer lies in the Pacific Ocean on the other side of the globe. While rising magma at the mid-Atlantic ridge expands the Atlantic, the same is happening at the mid-Pacific ridge, only bringing different results. Since there is no more room to accommodate the Pacific Ocean’s crust, the oceanic crust must choose a downward subduction at the junction of land and sea, right were the trenches are located. Here, the oceanic crust goes underground and is melted into magma by the high temperature of the mantle. Therefore, as the magma at the mid-Pacific ridge propels the oceanic crust to expand, the Pacific not only does not widen but also must undertake the expansion from the Atlantic Ocean, narrowing it continuously as a result. For these reasons, we will find few trenches along the Atlantic, while the Pacific Ocean is surrounded by trenches.
Seafloor spreading is a continuation and development of the continental drift theory, and plate tectonics was built on its basis. Scientists believe there to be several clear fissures on the earth’s lithosphere; they divide the earth’s crust into several units signaled by mid-ocean ridges, trenches, and faults, forming relatively independent plates. These plates float on the mantle’s asthenosphere and are propelled into constant movement by Earth’s internal heat. By moving away from or against each other, plates form mountains, canyons, rivers, ridges, trenches, and island arcs.
Earthquakes and volcanoes are closely related to the tectonics and movements of plates. Historical earthquake and volcano distribution data shows that plate boundaries are consistent with the dispersal of earthquakes and volcanoes. For example, China’s Taiwan and Japan’s Ryukyu Islands are prone to earthquakes due to collisions between the Philippine plate and the Eurasian plate, and the Luzon volcano arc is located east of the north Luzon trough formed by these collisions. Earthquakes also occur frequently in the San Francisco area of the United States, which is due to the movements of the Pacific and American plates.
The disaster brought on by earthquakes and volcanoes is both persistent and large-scale. To use volcanic eruption as an example, on August 24, year 79, the Vesuvius volcano in Italy erupted suddenly, burying the bustling city of Pompeii in an instant. More than a thousand years later, people discovered this buried city by chance. The dying moments of the city’s residents had been clearly preserved, and it was clear how frightened and unprepared they were. In 1902, the Pelée volcano on the Caribbean Martinique island erupted. During the initial eruption on April 25, volcanic ash and steam shot into the sky, and the rumbling echoed into the distance. Residents of Saint-Pierre, ten kilometers away, watched this rare spectacle excitedly for days. However, on May 18, the volcano became suddenly violent and the eruption height rose to several hundred meters. Volcanic ash containing toxic gas bore down over Saint-Pierre. The beautiful harbor city lit up in flames, killing all 28,000 people; only one prisoner and one shoe repairman survived. Afterwards, it was learned that the prisoner survived because he was kept in an enclosed semi-basement; none of the police guarding him were spared.
The earthquakes produced by plate activity are even more destructive, such as the famous Japanese Kanto earthquake that resulted in 143,000 deaths. The earthquake that claimed the most lives in the past century was the Chinese Tangshan earthquake that occurred in the Tangshan city of Hebei province. At 3:43 in the morning on July 28, 1976, a 7.8 magnitude earthquake shook the slumbering city and destroyed the industrial city of Tangshan in mere seconds; 242,000 people were killed and 164,000 were seriously injured.
The Wenchuan earthquake that took place in Sichuan, China, was another deadly disaster. On May 12, 2008, at 2:00 p.m., the collision of the Indian plate and the Asian plate resulted in an 8.0 magnitude earthquake in the mountains of Sichuan. The destruction and scope of this earthquake surpassed even the Tangshan earthquake. The capital, Beijing, thousands of kilometers away, as well as neighboring Thailand, Myanmar, and other countries, all felt a significant shock. Ninety thousand people died or went missing, and more than three hundred thousand were injured. Thirty barrier lakes were formed in the alpine canyons. If this earthquake had occurred at night or in a densely populated area, the casualties would have been even more unimaginable.
Earthquakes and volcanoes also lead to tsunamis and fires. The 1923 Tokyo earthquake struck during lunchtime; the shocks from the earthquake overturned stoves and ignited over two hundred fires. More than one hundred thousand people were burnt to death.
The largest tsunami on record happened on December 26, 2004, when an 8.9 magnitude earthquake shook the seabed of the Indian Ocean near Sumatra, Indonesia. The ensuing tsunami ravaged Indonesia, Sri Lanka, India, Thailand, and more than a dozen other countries. Even the distant east coast of Africa was affected. Most of the areas affected by the tsunami were famous tourist destinations, and as it was tourist season, tourists from all over the world had gathered on the waterfront, unprepared for the devastating catastrophe. The number of deaths and disappearances caused by the tsunami eventually exceeded 225,000.
The 9.5 magnitude Chilean earthquake in 1960 was the largest earthquake ever recorded. It brought on a tsunami that produced waves over twenty-five meters high; 10.7-meter-high waves were recorded ten thousand kilometers away from the earthquake’s epicenter. The main tsunami spread across the Pacific to affect Japan, the Philippines, and other areas across the ocean.
No matter how much devastation earthquakes and volcanoes may bring, they only affect individuals and groups. The overall survival and happiness of humanity is not threatened.
We should actually adopt a more objective and scientific view of plate activity. There would be no mountains and rivers without plate activity, and thus no ecological cycle. Earth would lack vitality, and life would have difficulty developing and evolving in such an environment.
After studying the planets and satellites of the solar system, astronomers argued that Earth is the only planet that has plate movement within this star system. To take our satellite moon as an example, we can see that its surface is covered in craters formed three to four billion years ago. The earth exists in a similar environment to the moon, but the initial traces on Earth’s surface have mostly been updated and are no longer visible. It is Earth’s unique plate tectonics that grants this 4.6 billion-year-old planet energy, so it is an important factor in Earth’s development as a planet full of life and civilization.
In reality, plate activity benefits mankind even while it brings disaster. The formation of many important deposits is closely related to plate activity, and plate activity leads to the exchange of material and energy between the litho-sphere, asthenosphere, hydrosphere, and atmosphere, producing the variety of minerals that humans use every day.
Two: Climate Change and Glaciation
The normal climate change of Earth follows a pattern: winter is cold, spring and autumn are warm, and summer is hot. This is because different parts of Earth receive sunlight differently. Even along the equator, where temperature differences are smaller, there are rainy seasons and dry seasons. There are often years when the climate is abnormal, hot spells may last longer, or the cold season may be lengthened. These instances usually bring trouble; for example, global warming can cause floods, hurricanes, epidemics, or increased agricultural pests; and drops in temperature can affect agricultural production, freeze livestock to death, cause traffic jams, and injure people through avalanches and other disasters. However, these do not significantly affect the survival of humanity. Agricultural production will fluctuate from year to year, and problems like disease, floods, and avalanches do no endanger humanity as a whole. Alternating seasons are especially beneficial to humans; they enrich our lives, and winters provide relaxing respite after the long planting and harvesting seasons. This has been the way of our ancestors for centuries. At the same time, everything should abide by a limit. Once this limit is surpassed, good things may become disasters, and tens of thousands of years of heat or cold would be a completely different situation.
The surface of Earth not only has seasonal changes, but also goes through long spells of extreme heat or cold from time to time. Sometimes these long spells last tens of millions or even hundreds of millions of years. Seven million years ago, the earth experienced a period of extreme cold, and snow and ice covered most of the globe for tens of millions of years. Even the equator showed traces of glaciers. One hundred million year ago, the earth also experienced a period of extreme heat. For tens of millions of years, ice melted in the two poles; Antarctica and Greenland were as warm as spring, and even dinosaurs roamed there.
The earth constantly fluctuates between hot and cold, and scientists have discovered a pattern to this fluctuation. A long cold period usually occurs every 250 million years; this is called an ice age. The temperature is not static during this time; in fact, every ice age can be divided into several smaller glacial periods (or glaciations), and the warmer interval between consecutive glacial periods is called an interglacial period. Currently, we are in an interglacial stage of the Quaternary glaciation (also known as the Pleistocene glaciation, or the current ice age). In the two million years of the Quaternary glaciation, there have been several glacial and interglacial periods, but we do not feel the cold of the ice age since we are in an interglacial period.
The last glacial period started eighteen thousand years ago and ended ten thousand years ago. During that time, Greenland, Canada, Alaska, Siberia, Iceland, and most of northern Europe were covered in ice and snow. Large amounts of seawater were converted to snow and ice, resulting in a 150-meter drop in sea level. The Bering Strait disappeared and joined North America with Siberia; in Asia, the seabed of China’s Yellow Sea and Bohai were exposed; the Korean Strait and the Tsushima Strait disappeared; Japan became connected with Eurasia; and Indonesia joined with Asia. In Western Europe, seawater withdrew from the English Channel, and the British Isles became part of the European continent. Australia connected with the Asian continent through a land bridge.
Scientists have done much research on the earth’s alternating glacial periods, and there are many differing views concerning its cause. For example, some people think that the uplifting of the Himalayas from the sea caused carbon dioxide in the air to combine with rock rising from the ocean, lowering the carbon dioxide content in the atmosphere and causing a drop in global temperature. Others believe there to be a dense interstellar cloud along the sun’s orbit around the Galactic Center that partially covers the sun and changes Earth’s surface temperature (though it is not visible from Earth to the naked eye). This theory is supported by the fact that ice ages share the same 250 million years cycle as the sun’s rotation around the Galactic Center. None of the current views can fully explain the fundamental cause of ice ages convincingly. It is most likely that ice ages are the result of a combination of factors, including some that we may not yet recognize.
The larger climate change cycles of Earth affect global ecology and human life, but they do not affect the overall survival of humanity. Global climate change happens gradually, not suddenly. In a glacial period, ice first covers the two poles and then extends from higher latitudes to lower latitudes. The higher latitudes of both the north and south hemisphere are not suitable for human habitation or farming; however, as ice and snow coverage expands, the sea will retreat and land will be exposed to create areas suitable for human habitation and agricultural production. Oxygen dissolves easier in colder seawater, making it more conducive to the growth of marine life, which is why the polar regions are swimming with fish and shrimp. Whales, seals, walruses, and penguins all survive in the polar regions due to a rich marine life food source.
As the global temperature continues to climb and melt the polar ice sheets, and sea levels rise and erode coastal lowlands, there seems to be less space for human habitation and farming. That is not the case. As temperatures increase and snow melts, the Antarctic continent and Greenland will become suitable for living and planting, and the originally harsh environments in northern Siberia, northern Canada, and northern Scandinavia will become pleasant pastures and farmlands. The increase in land also includes the land that had previously been pushed thousands of meters under water by ice sheets. Once the snow melts, they will rise continuously until they reach the surface. The rise in temperature will also be beneficial to plant life and animal reproduction. Climate change is able to maintain a balance on Earth; the ecological environment and humans’ habitation space will not change too drastically as global temperatures rise and fall.
Even if we take the situation to the extreme and reimagine the ice age of seven hundred million years ago when glaciers spread to the equator, the overall survival of humanity would not be in danger. The development of science and technology today is enough to produce fresh fruit and vegetables in greenhouses during the dead of winter, providing us with enough confidence to overcome glaciations.
In the two million years since the Quaternary glaciation, humans have evolved from ordinary people to Homo sapiens. Animals evolved thicker skin and longer hair to combat cold weather, but humans developed less and less body hair because we learned how to use animal skins as clothing and how to gain warmth from fire. Our brave ancestors did not flee to the warmth of the equator in the face of cold weather; instead, they moved boldly to Asia and Europe and survived in the more severe conditions there.
The cold of the glacial period caused ice to cover the higher latitude areas, and sea level to drop more than one hundred meters, causing the Bering Strait to vanish and forming the land bridge between Asia and Australia. Humans entered Australia via the land bridge and migrated to the Americas through the Bering Strait, spreading human footprints over the entire world.
Many creatures were unable to withstand the cold of the Quaternary glaciation and went extinct one by one, but humans continued to evolve and strengthen in the struggle against nature. Those primitive conditions did not destroy the ancestors of man; thus, we have no reason to fear that modern humans, who have higher degrees of wisdom and advanced science and technology, will succumb to the cold.
Simple life-forms existed on Earth 4.28 billion years ago, complex life evolved in the ocean 530 million years ago, and a variety of creatures came onto land 400 million years ago. During this period, the earth went through numerous glaciations and many species died out, yet life has continued to this day without interruption. Earth today has more wisdom and civilization than ever before, which shows us that glaciations are nothing to fear.
Three: Magnetic Field Disappearance
Space is full of cosmic rays that originate from high-energy particles and attack our planet incessantly at a speed close to that of light. If humans or other creatures were directly attacked by cosmic rays, the high-energy particles could penetrate cells—not only killing the cells but also changing or destroying genetic material.
We generally do not suffer the harm of cosmic rays because Earth’s surface has three layers of safeguards against them. The first safeguard is Earth’s surface atmosphere, which also happens to be the most powerful barrier. When cosmic rays travel to Earth at high speeds, they collide with the molecules and atoms in the atmosphere. After every collision, the cosmic ray’s energy decreases. Once the energy particles reach Earth, their energy level is so low they cause minimal damage to humans.
The earth’s magnetic field is another safeguard. When cosmic rays pass through the magnetic field they must use their energy to overcome the magnetism within the field. Some lower energy cosmic rays will be captured by Earth’s magnetic field without ever reaching Earth’s surface, while higher energy cosmic rays will also suffer great damage by the time they pass through. Earth’s magnetic field is the secondary barrier outside the atmospheric barrier.
The final layer of protection against cosmic rays is the interplanetary magnetic field from the sun. This field wraps around Earth’s magnetic field and serves a similar function in consuming the energy of cosmic rays. This magnetic field is vitally important in protecting life on Earth, yet long-term observance shows that the field is not always stable. It fluctuates in strength, swaps between north and south magnetic poles, and sometimes vanishes altogether, leaving Earth vulnerable. To consider the effects of geomagnetism disappearing, we must first understand the basic nature of geomagnetic fields.
In physics, we all know that electricity and magnetism can interact in a phenomenon called electromagnetism; that is, electricity can sense magnetism, and vice versa. Earth’s core is partially composed of molten iron and nickel; this liquid metal moves in a rotating motion within Earth’s core due to Earth’s rapid rotation. This is as if a giant electrical current were flowing underground, producing a strong magnetic field, which is Earth’s magnetic field.
The study of paleogeography found geomagnetic fields to be changing following this pattern: geomagnetic poles are located close to Earth’s poles. The intensity of the magnetic field will gradually weaken after passing the strongest point, disappearing briefly before gaining back its former strength. The magnetic poles will be reversed during this cycle. In the past seven hundred thousand years, Earth’s magnetic field has followed its current direction, but it was reversed in the 450,000 years before that. After studying the geomagnetic field’s movements over the past one hundred million years, it was discovered that the magnetic poles reverse every four hundred thousand to five hundred thousand years. The shortest reversal period was fifty thou-sand years.
A reasonable explanation for magnetic pole reversal has been proposed: it is caused by the flow direction change of molten iron and nickel in Earth’s core. The iron and nickel in Earth’s core does not always flow in one direction once the flow direction reverses Earth’s magnetic poles reverse accordingly. During the moment of critical pause when flow direction is changing, geo-magnetism will vanish briefly. Since the flow of molten iron and nickel at Earth’s core follows Earth’s rotation, the magnetic pile will not deviate far from the two poles, no matter its orientation.
What happens to Earth during the brief period of geomagnetism disappearance? One thing is for certain; under normal circumstances, cosmic rays and solar particles cannot cause lethal damage to humanity due to the protection from Earth’s atmosphere. In the four million years of human evolution, the Earth’s magnetic field has disappeared briefly numerous times without affecting mankind or other Earth creatures very much. Through research of atmospheric protection against cosmic rays and solar radiation, scientists have proven that geomagnetism disappearance will not have a decisive impact on the survival of humanity in normal circumstances. What about the unusual circumstances? In the next few billion years of human survival, unusual circumstances are likely to occur.
The most important sources of cosmic rays are supernova events in the Milky Way. Every supernova of considerable scale releases cosmic rays tens of thousands of trillions of times that of the sun. What would happen if a supernova event took place not far from us? Studies have shown that with the protection of the atmosphere, Earth’s magnetic field, and the sun’s magnetic field, high-intensity cosmic rays cannot compromise human survival as long as the supernova event is more than twenty-five light-years away. However, if Earth’s magnetic field disappeared at this critical moment, the situation would be much more severe. With the disappearance of geomagnetism, the earth would suffer attack from both solar particles and cosmic rays; the earth’s atmosphere and the sun’s magnetic field would not be enough to withstand such a double attack. Therefore, the safe distance would have to be pushed back to thirty light-years. Moreover, geomagnetism changes today indicate that a brief disappearance of Earth’s magnetic field will occur in the next ten thousand years.
In the next ten thousand years, the most likely supernova event close to Earth is Betelgeuse. Fortunately, Betelgeuse is 640 light-years away, meaning that Earth’s atmosphere and the sun’s magnetic field would offer sufficient protection, even if the outbreak coincided with geomagnetic field disappear-ance. In fact, there is no possible supernova within thirty light-years of us, and scientists have determined the probability of a supernova within that distance to be once every ten billion years. With such a small window of opportunity, it is extremely unlikely that such an event will occur simultaneously with geomagnetism disappearance.
Even if such an unlikely coincidence were to occur, we would not need to worry. Firstly, with Earth’s atmosphere and the sun’s magnetic field serving as two shields, cosmic rays produced by a supernova within close distance would be sufficiently weakened so as not to endanger the overall survival of mankind. Secondly, the strong cosmic rays generated by the supernova would not last long (a few weeks at most), and there would be warning signs in advance so that proper arrangements could be made to avoid injury. The walls and roofs of our houses can all offer protection from cosmic rays. As long as we properly fortify our dwellings and limit outside exposure, we can avoid being harmed by cosmic rays.