What kind of planet is our Earth? Its characteristics are easily visible when seen from the outer space. With blue oceans and trailing clouds, Earth is a planet covered with water. When a star like the Sun is born, remaining nearby dust can clump together and form small planets like Earth. When one is formed closer to such a star, it becomes a hot, burning planet of fire. When one is formed far from the star, it becomes a cold, frozen planet. Earth has liquid oceans simply because it was coincidentally formed at exactly the right proper distance from the Sun, where it is not too hot or too cold.
The chances of an ocean planet, like Earth, being formed a proper distance from a star is believed to be about 1%. Earth was born under a probability of only one in one hundred.

Meanwhile, there are 200 billion stars in the Milky Way, the galaxy that includes our Solar System. A simple estimation suggests that there may be 1% of 200 billion, or two billion, ocean planets in the Milky Way. Moreover, the Milky Way is just one of the innumerable galaxies in the universe. Probability suggests there are many more Earth-like planets in the universe.
But are these other Earths full of life like ours?
Today, I’d like to talk about how life was born on our planet Earth, and how it achieved its current form, teeming with life. By watching the evolution of both Earth and life itself, let’s consider whether we really are alone in the universe, or if life like ours could be incredibly common.

The four-billion-year evolution of both life and Earth was no gentle stroll up an even slope. Instead, it involved dramatic convulsions and several epochs of ups and downs. I am going to take us through these epochs, each one key to the destiny of the Earth. We’re also going to evaluate the present from the perspective of evolution of life on Earth, and then think about the future, which starts from this moment.

Today, Earth is home to several tens of millions of species of life. It includes huge terrestrial mammals like elephants, fish and crustaceans deep in the sea, flying insects, and practically invisible microorganisms like bacteria. Life is diverse not only in size but also in habitat.

This diversity is a result of the evolution of life, which has spanned the extraordinarily long period of four billion years. At the same time, it is not the result of the self-willed evolution of organisms. Instead, it is a consequence of the dramatically evolving Earth, each challenging new environment thus created, and life having to continue to change flexibly and vigorously to keep up. Those that could not adapt disappeared—what we call becoming “extinct.” Far more species have gone extinct in the history of the Earth than currently live on our plant today.
The first epoch in the story of life on Earth is the beginning of life, or the origin of life. Much like how a big river starts from a drop of water seeping out from a mountain, all our diverse lifeforms started from one single common origin.

Life on Earth is believed to have been born about 4.2 to 4 billion years ago. I say “is believed” as there is no absolute evidence that proves when life began on Earth. The oldest marine sedimentary rocks remaining on our planet are 4 billion years old, meaning there is no older data. Because life existed already four billion years ago, life must have been born at least that long ago.
Meanwhile, Earth was formed 4.5 million years ago. Early Earth was first covered by high-temperature magma oceans. Later, when the magma started to cool down, the atmosphere and oceans were formed. During the first several hundred million years, however, Earth was subjected to frequent massive asteroid impacts, which likely caused all the oceans to evaporate. It was only about 4.2 billion years ago when an environment ready for the beginning of life was finally shaped.
Exactly where and how the life on Earth was born is a question for which no one knows the true answer, as there’s no conclusive evidence. Despite this lack, many scientists agree on a location that is likely the key—these being underwater hot springs, scientifically called “hydrothermal vents.”

Three elements are essential for life to survive; organic matter, water, and energy. Comparing life to an analog clock, organic matter are the parts constituting the clock, such as gears and screws; water is the lubricating oil that smoothly connects the components; and energy is the battery. A clock can function only when these three are assembled, and the same applies to life. Life can perform biological activities—those activities particular to life, such as cell division and metabolism—when the three elements are available.
One of the reasons why hydrothermal vents are a key in studying the origin of life is that these three vital elements are naturally available there. Of them, energy, is the most important. Like a clock, which stops functioning when the battery goes dead, life dies quickly when there is no energy available.

In and around hydrothermal vents, hot water touching rocks causes chemical reactions that involve the formation of molecules such as hydrogen. The products of such reactions between hot water and rocks serve as food for primitive lifeforms. All primitive organisms that currently live on Earth feed on hydrogen, produced through reactions between hot water and rocks, and gain energy. They settle on rocks and receive a tiny proportion of heat energy from Earth to power the analog clock of life.
At the eve of abiogenesis, when life emerged from non-living matter, diverse kinds of molecules were formed in and near hydrothermal vents through reactions between rocks and hot water. From such molecules. complicated organic substances that had functions much like life emerged and are believed to have evolved into primitive life. This was the “beginning of life”.

Primitive lifeforms born in hydrothermal vents first lived a weak and meagre existence. Soon they became accustomed to the environment and started to propagate. The propagation continued until the hydrogen and geothermal energy available at the thermal vents became insufficient to support them. Individual organisms that actively propagated left many offspring. As a result, such aggressive individuals could preferentially survive. The survivors were not weak and meagre anymore.

Before long, the number of microorganisms reached the limit of the life-nurturing capacity of the origin hydrothermal vent. Some left the vent, being displaced or simply being engulfed by oceanic currents. These microorganisms drifted about in the sea. They could not swim and so were adrift, leaving their life to fate. A few lucky ones reached another hydrothermal vent. Most of the microorganisms perished in the foodless desert of the sea.
Interestingly, there emerged some that expressed a miraculous ability that we call photosynthesis. An organism’s substances for detecting light underwent changes and became able to use solar energy to break down the surrounding water and produce hydrogen. Hydrogen is the food produced in a hydrothermal environment—in other words, an energy source. For the first time, life acquired the capability to create energy without hot water, from sunlight.
Photosynthesis is one miracle in the evolution of life. The chances must be minute that a mutation occurs in the gene of a drifting microorganism so that molecules enabling photosynthesis are created!

Photosynthesis is believed to have emerged about three billion years ago and is one of the most important biological innovations by life on Earth. Until then, life relied on the heat of the Earth for its energy. With photosynthesis, it became possible to use sunlight as energy instead. This innovation freed organisms from life crowded around small and local hydrothermal vents deep undersea, and allowed them to simultaneously spread to all parts of the world exposed to sunlight. This is known as the spread of life.
However, the emergence of photosynthetic organisms alone did not immediately lead to the entire Earth becoming full of the life. Another major event also had to occur. This was the global glaciation that occurred about 2.5 billion years ago, called a snowball Earth event, and during which the entire global surface was covered by ice.

The snowball Earth glaciation was a key event because of the intense greenhouse effects that occurred as a reaction immediately after the glaciation period. In this resulting ultra-greenhouse climate, the population of photosynthetic organisms exploded. As prior primitive organisms once propagated to the upper energy limit of their hydrothermal vent homes, photosynthetic organisms propagated to the upper limit offered during the greenhouse Earth. Photosynthetic organisms spread throughout the globe and rapidly filled the atmosphere with oxygen, a byproduct of photosynthesis.

This Great Oxidation Event occurred about 2.5 billion to 2.2 billion years ago and still marks the worst environmental pollution in the history of the planet. Oxygen was highly toxic to microorganisms. Most of them died out, and those survived shifted their habitat to the silt of the deep-ocean seabed, where oxygen could not reach. Atmospheric oxidation—the increase in oxygen content of the atmosphere—also caused changes in the chemical composition of oceans. Oxygen caused reduced iron dissolved in the oceans to precipitate on the seabed as oxidized red iron deposits. Sulfur became a major component in the oceans because the presence of oxygen increased its supply. Such drastic changes in marine water composition caused far-reaching changes to the ecosystem of the time.
Meanwhile, life also emerged that adapted to the oxygen-rich environment and efficiently used the gas for respiration. These are the ancestors of humanity, eucaryotes. Respiration using oxygen produces enormous amounts of energy. Comparing life with our analog clock once again, if the energy acquired at a hydrothermal vent is deemed a button battery, then aerobic respiration—using oxygen—produces energy enough energy to move an automobile. Just like a larger battery being able to move a larger machine, life that acquired aerobic respiration became larger and more complex by using that same energy.

Earth experienced global glaciations and became the snowball Earth again about 600 million years ago. Immediately after the glaciation periods, a similar massive propagation of photosynthetic organisms and second oxidation of the atmosphere occurred. The second oxidation event caused multicellular life to emerge. Multicellular organisms expanded their habitat from the sea to the land, backed by their motor capabilities powered by high energy from the higher oxygen concentration. Finally, the spread of life came to cover the entire globe, including the land.

The three essential elements for life: organic matter, water, and energy. A revolution in gaining energy, called photosynthesis, in turn causing environmental pollution of global scale. And life that adopted to the change being able to rapidly expand their habitat.
Similar phenomena can be said to be happening due to the human industrial revolution and mechanized civilization. From the perspective of the four-billion-year history of life on Earth, if we call the period when life relied on the heat energy from Earth the first epoch, and the period of using sunlight energy the second epoch, we currently find ourselves in the third epoch.
Humanity uses fossil fuels and atomic power to gain energy. This means that, which previous organisms used energy that was available only in the moment, humanity can freely obtain energy from the past and future, surpassing the flow of time. Fossil fuels are preserved solar energy from the past. Atomic power involves gaining energy by artificially accelerating nuclear fission that may occur in future.

Acquisition of energy that surpasses time has enabled humankind to power automobiles and trains, construct huge cities and tall buildings, and launch space ships into outer space. It is basically the same as previous organisms increasing the size and complexity of their bodies and earning higher motor capabilities.
Human civilization is one of the most important innovations made by life on earth, closely equivalent to the acquisition of photosynthetic ability by those simple lifeforms in the distant past. Current global warming and environmental changes may be comparable to the environmental pollution caused by the Great Oxidation Events.

As the stages of energy acquisition have advanced, life has expanded its habitat dramatically. From that perspective, it may be an inevitable consequence of the evolution of life that we have developed our current civilization and are spreading our living sphere to the Moon and eventually to Mars.

I am neither negative nor pessimistic about human civilization, which marks the third epoch. My point is that the period called the “present” may give a different impression when it is seen from the history of life on Earth.
The future of life and the third epoch has just started, and we are all are a wonderful, integral part of this period. Humanity is fundamentally different from hydrothermal vent-dwelling microorganisms and photosynthetic organisms, in terms that helping each other and sympathy for each other have become basic building blocks for us to live as social multicellular organisms. I believe that humankind will be able to survive in a manner different from those of lifeforms that marked the past two epochs.
There must be a vast number of ocean planets, like Earth, out in the universe. There may even be some on which civilization has evolved. An awareness of these universal possibilities may come to alter our way of living in interesting ways.

Other than our Earth, are there planets in the universe that harbor life? Let’s talk about the forefront of the search for life in the Solar System.

First, how should we even be searching for life in the universe? As I discussed previously (“The Four-billion-year Story of the Life on Earth”), three elements are essential for life to survive on Earth. They are organic matter, water, and energy. On Earth, life always exists where the three can be found together.

The first step in the search for life in the universe is therefore finding astronomical bodies that also have these three elements. One of the major objectives of exploring the Solar System, which started in the 1970s, has been to discover planets that can harbor life by finding these elements present there. We started by looking for liquid water, followed by seeking organic matter and energy. In the 2000s, NASA’s keyword for Solar System exploration was “follow the water.” Today, that has evolved into “follow the carbon,” as carbon is the basic building block of both organic matter and energy.

This 50-year-long project has discovered liquid water and its traces on many astronomical bodies in our Solar System besides Earth. Organic matter and energy have also been detected on several bodies, suggesting that the discovery of extraterrestrial life might be close.

Candidates for those that might harbor life are Mars, Europa (Jupiter’s moon), and Enceladus (Saturn’s moon). Mars is the destination of Mitsubishi Miraikan’s “Journey to Life.” It is a neighboring planet to Earth and slightly smaller in size. Because it’s a little farther from the Sun, the surface is cold, with a mean air temperature of -50°C. But during summer, the temperature sometimes reaches about +15°C. It has an atmosphere, although it’s about 100 times thinner than Earth’s. So, it’s a cold planet of vast red deserts—but also a good starting point when discussing our search for life.

Many spacecrafts have been sent to Mars; more than to any other astronomical body. Orbiters orbit the planet, take photos of the surface, and investigate the materials found there. The Mars Reconnaissance Orbiter reached Mars in 2006 and is monitoring the surface at a surprisingly high spatial resolution of 30 cm.

The high-resolution images of the ground surface tell us many things. There are traces of landforms created by water, such as rivers and lakes, definitive evidence that Mars was once a water planet. Clay minerals and salts, which are formed under the presence of water, have also been found on the river and lake beds, showing that the planet once had abundant water.

Clay minerals and salts are not only evidence of the existence of water but also preserve information about the environment of the time they were formed, such as the temperature and amount of water. This evidence of landforms, clay, and salts as created by water have been found at several thousand locations on Mars. We have also determined the approximate period of their formation. These environments were analyzed from the data shown by clay minerals and salts and arranged into chronological order to draw up a rough chronological table of the history of Mars’ environment; that history is as follows.

What caused these changes in its environment? It is believed that, because Mars is smaller than Earth, its atmosphere escaped from its gravity out into space, and volcanic activities, which could have helped refill that atmosphere, also declined. Meanwhile, Earth has a larger size and has maintained volcanic activities, thus being able to remain a water planet. Those same volcanic activities have also completely erased any records prior to 4 billion years ago, when life started on Earth. On the contrary, records from that long ago remain abundantly on Mars, where volcanic activity stopped. We might find traces of the start of life on Mars, which have been lost on Earth. This is one of reasons that exploring Mars is so fascinating.

Of the three elements of water, energy, and organic matter, Mars definitely had water at least 3.5 billion years ago. Sunlight, which is energy, reached its surface. The final element is therefore organic matter. Did organic matter, the building blocks of life, once exist on Mars?

Data from Mars orbiters alone are insufficient to answer this question. Organic matter could exist in the soil in small quantities, meaning precise analysis via a lander or rover is indispensable.

Huge rovers weighing almost 1 ton have already landed on Mars. These rovers monitor the soil with microscopes, collect specimens, and investigate them using diverse analytical equipment. It’s like sending a robotic scientist over to Mars!

Curiosity Rover landed inside Gale Crater, which was a lake 3.7 billion years ago. It started collecting and analyzing the mud and sand that accumulated on the ancient lake bed.

Curiosity analyzed Gail Crater sediment samples and found organic matter in all samples. When there was a lake in the crater, organic matter coexisted with the water, and has since been preserved within a mud time capsule. This also happens on Earth, with microorganisms that inhabit lakes being preserved as organic matter in lake sediment. We therefore discovered that organic matter joins water and energy as once existing widely on Mars. This discovery was made in 2019.

Even more surprising were the components of the organic matter. It contained large quantities of sulfur. There is almost no organic matter on Earth that contains so much sulfur. Organic matter contained in mud on Earth is almost entirely of organism origin and contains elements such as carbon, nitrogen, oxygen, and phosphorus. The organic matter on Mars contained scant nitrogen and phosphorus but abundant sulfur.

We still do not know whether this organic matter is a trace of life on Mars or a trace of organic matter prior to the birth of life. At least, we can imagine that if life was born on ancient Mars, it might be different from life on Earth at an elemental level. If we can discover life that has different elements from life on Earth, we will be able to recognize that life here is just one type from a diverse range, and understand what “life” is from a wider perspective.

Numerous landers have reached the surface of Mars. There are also plans to bring back samples via robotic missions, as well as plans for Human exploration of Mars. As shown in “Journey to Life,” parts of the seas and lakes that once existed on Mars are believed to remain frozen underground. Precise analyses of such specimens, either on Mars or back on Earth, are expected to unveil whether such cryopreserved organic matter in ancient sediments such as mud, sand, or frozen soil are actual traces of life.

Now, let’s continue past Mars and go to the outer Solar System. There, the sunlight is weak, creating a frigid world. Icy moons orbit around Jupiter and Saturn. They look like snowballs floating in space. The surface is below -150°C; a temperature at which not only water but even carbon dioxide will freeze.

You may think it impossible to find seas, let alone life, in the frigid outer Solar System. However, liquid water has been discovered to exist as subsurface oceans on several icy moons.

The first astronomical body that was found to still possess liquid ocean besides Earth was Europa, one of the moons of Jupiter. There are almost no impact craters on Europa’s surface. Any such craters have been erased by gushers of subsurface ocean water and the subsurface ocean moving the surface ice.

When we observe Europa carefully, we notice there are reddish lines running in all directions. These bands are evidence of Europa having subsurface oceans. The red material is salt covering cracks on the ice surface. When water from a subsurface ocean squeezes out through a crack, it freezes immediately when it is exposed to outer space. The salts contained in the water turn reddish and form these bands.

Europa orbits Jupiter along a slightly oval orbit. It therefore deforms when it comes closer to Jupiter, due to Jupiter’s massive gravity, and then restores its shape when moving further from the planet. The deformation produces frictional heat inside the moon rock, melting the ice and creating a rich subsurface ocean even on a frigid world.

Enceladus is one of icy moons of Saturn. It is a small moon, 500 km in diameter. This little body also has subsurface ocean like Europa. Moreover, the water spews out from cracks on its south polar surface, reaching into space like a geyser.

NASA’s Cassini spacecraft passed through Enceladus’ geysers several ten times before it completed its mission in 2017. This marked the first time in human history that we sampled extraterrestrial oceanic water. The water was found to contain salts, gases such as carbon dioxide and ammonia, and organic matter, including simple molecules like methane and complicated ones as big as a microorganism. In other words, Enceladus was discovered to have two of the three elements for harboring life, water and organic matter. What about the third, then? What about energy?

Hydrothermal vents on Earth are places where sunlight does not reach but that harbor primitive microorganisms using geothermal energy instead of sunlight. As mentioned in “Journey to Life,” these vents were considered to be the birthplace of life on Earth. Could the same hydrothermal environment exist in the subsurface ocean of Enceladus, where sunlight does not reach?

In 2015, this question was answered. Nanoparticles of silica were discovered in Enceladus’ geyser water. Precise analysis showed that there are hydrothermal vents at the bottom of its subsurface ocean and that the particles were formed by rock components having leached into hot water at the vents.

Enceladus therefore has the three elements essential for life. It is the first place beyond Earth where an environment that can currently harbor life has been proven to exist. The moon is suddenly receiving attention as a valuable astronomical body that can maybe realize one of the ultimate goals of science: finding living extraterrestrial life. While continuing to investigate Mars, plans are being drawn up to land on Europa and Enceladus, and to search for life by approaching cracks in the ice where ocean water surfaces or spurts out as geysers.

As I mentioned at the beginning, the three elements that harbor life have now been discovered in the Solar System. In the 2030s, a full-scale search for life will start on these astronomical bodies. Projects will involve robotics, bringing back samples, and then human exploration. I’m optimistic that we will find life on several bodies.

However, there may also be those that have the three elements to harbor life but where there is no life present. In that case, the next question will arise: why does life not exist there?

We know the conditions for life to exist, namely, energy, water, and organic matter. This knowledge has been acquired by observing life on Earth and combining that with what we learned by investigating environments that harbor all life. We know the conditions where life can survive but do not know the conditions for life to be born. The conditions for starting life may need something more than just the conditions for its survival.

For example, let’s assume that life is discovered on Mars but not on icy moons such as Europa and Enceladus. What does Mars have that the subsurface oceans of the icy moons do not? Atmosphere, landmass, and sunlight. Maybe, chemical reactions within the atmosphere and concentration of organic matter on land are necessary for life to be born.

Hydrothermal vents are the strongest candidate for the place where life on Earth started. But of the molecules that reached there and were used for building life, there may have been those that formed in the atmosphere or on land. Even though there are hydrothermal vents on the icy moons, they are not identical to those found on primitive Earth.

I am hopeful that we will soon be able to advance the ultimate mystery of the birth of life, through either the discovery of life or no life in these places.

At the same time, if we discover that life has indeed been born on Mars or an ice moon, we will know that this universe, inside and outside the Solar System, is full of life and we, life on Earth, are not alone.

In 1995, humanity detected a planet outside the Solar System for the first time in our history. A planet was found orbiting around a shining star, which emits light like the Sun.
Many attempts had been made to search for planets beyond the Solar System, but they had always been unsuccessful. The first discovery was made when astronomers were just to give up, almost concluding that planets like Earth were likely to be very rare in the universe.

Since that first discovery, many exoplanets—planets outside the Solar System—have been detected by astronomists from all over the world. Indeed, more than 5000 exoplanets have been observed. It is now believed that the birth of a star inevitably involves formation of a surrounding disk of gas, in which planets are also born. Every star we see in the night’s sky may have a planet—or planets—orbiting around it.

Several Earth analogues have been detected, which have a size comparable to Earth and orbit in the habitable zone, or at a distance where liquid water can exist. Is there life on these planets, essentially Earth II or Earth III? Is it possible that there’s intelligent life and a civilization flourishing on them? Today, let’s dig deeper into research on finding planets and life outside the Solar System.

The James Webb Space Telescope (JWST, hereinafter “Webb”) was launched in December 2021. Being the largest space telescope in history, the Webb has a 6.5-meter-diameter primary mirror, equivalent to the length of a microbus. It is a huge telescope floating in the space.
One of the Webb’s mission goals is to monitor the atmosphere of exoplanets. By turning its primary mirror toward several exoplanets that have been detected in habitable zones, the telescope continues its observations today.

One of exoplanets drawing astronomers’ attention is K2-18b. The planet was discovered to contain water vapor in its atmosphere even before the Webb started observation and may have oceans on its surface.

What projects will follow the launch of the Webb? Astronomers are planning to observe not only the atmosphere but also the surface of these exoplanets.
As already mentioned, it is difficult to directly observe an exoplanet with a telescope because of the strong light from its star. But this means it will be possible to observe an exoplanet directly if we can find some means to block the light from the star.
A key device for achieving this is a coronagraph. Simply put, this instrument acts like an eye mask, blocking out the light from the central star to allow observation of the exoplanet itself. If we can observe an exoplanet directly, we can see not only the atmosphere but also the underlying planet surface. We can investigate if there are oceans, landmasses, and light absorption by photosynthetic organisms or plants.

No space telescopic observation has ever been conducted using a coronagraph. The Habitable Worlds Observatory (HWO) is a space telescope to be launched after the Webb and is expected to realize just such an observation.
Let’s imagine for a moment that we will be able to observe the surface of an exoplanet using a coronograph. What kind of organisms might we find there? There have also been studies to estimate the characteristics of such organisms potentially out there in the universe. For example, the Sun around which Earth orbits is a G-type star, which emits light mainly consisting of the yellow spectral band. This is why Earth is covered by green photosynthetic organisms—why plants are green. A green pigmentation is optimum for absorbing the light of nearby wavelengths of yellow rays.
Meanwhile, the most common type of star in the galaxy is the M-type. Such a star emits light mainly consisting of red and infrared spectral bands. Plants on planets of an M-type star may therefore have developed pigments to better absorb red and infrared rays, and can be predicted to look like black plants to our eyes.
Stars that are bigger than the Sun, or B-type stars, emit blue light. Plants on planets orbiting around such a B-type star can be predicted to have a silver color.
Plants on exoplanets may have diverse colors depending on the type of their star.
If the surface of a planet is covered by substances that have mysterious absorbance, different from that of rocks, metals, or oceans, but like that of plants, then it will be biosignature; far stronger than anything relating to atmospheric components.

Which gives rise to the question—why haven’t we been able to detect extraterrestrial civilizations?
One of the possibilities is that the civilization of the life on Earth is exceptional in our universe. Life has not emerged on any other planet, or has emerged but remains still primitive, inhabiting near hydrothermal vents and has not reached the stages of photosynthetic life or subsequent multicellular organism, not to mention having spread across the planet.
Another possibility is that there are civilizations, but they are completely different from ours, with structures and development that we have never imagined. Therefore, our observation methods cannot detect them.

The first exoplanet was detected in 1995. We did not detect one prior to this because we assumed a planetary system exactly like our Solar System and tried to find that. The first detected exoplanet was completely different from the planets in our Solar System in terms of orbit and size. Diverse exoplanets were detected only after we freed ourselves from the existing idea of the Solar System. Likewise, we might be able to find civilization in the universe when we free ourselves from the concept of terrestrial civilization. At that time, our concepts of civilization and life will be completely revolutionized.

The last possibility is the lifespan of any given civilization. For a civilization to be detected by observation, the civilization needs to exist on the planet exactly when we turn the telescope to it. Civilizations are unlikely to last forever. It is difficult to think that one might be maintained over a period of billions of years, when we question how long we can keep our human civilization going by overcoming wars and other global issues.
On the contrary, durations like 500 and 1000 years might be a more realistic lifespan for a civilization. Supposing that civilization has a lifespan of 1000 years, one on an exoplanet can only be detected when its 1000-year period coincides with that on Earth, across the entire 13-billion-year long history of the universe.
After all, a civilization develops powered by avarice. As any civilization advances, it will inevitably reach the capacity of its home planet.

If we discover civilizations outside of Earth in the future, that civilization will have kept developing even after reaching its home planet’s capacity by overcoming or reconciling any issues preventing that. If it was possible for that civilization, human civilization on Earth might be able to do the same. The detection of an extraterrestrial civilization would provide evidence of the persistence of civilization over astronomically long periods of time and would also provide us hope and courage for our own future.