Reprinted
from the January 2011 issue of Amateur Astronomer
Author: Zhong Wanqing
The Emergence of Life is an Inevitable Consequence of Celestial Evolution
In the 15th century, the Renaissance in Europe sparked a revolution in humanity’s view of the universe. One of the primary proponents of Copernican theory, the Italian thinker Giordano Bruno, explicitly promoted the heliocentric model and raised the question of whether “extraterrestrials” existed. He wrote: “There are countless suns in the universe, and countless earths revolving around their own suns, just as our seven planets revolve around our sun…. These worlds are inhabited by various living beings.” The scientific master Galileo was the first to point a telescope at the starry sky, leading to a series of astronomical discoveries over the following centuries. The vast expansion of our cosmic perspective often prompts humans to ask: besides Earth, do other civilized planets exist in the vast universe? If they do, can we find a kindred spirit—intelligent life?
By studying terrestrial fossils, scientists have discovered that as early as 3.5 billion years ago, a relatively advanced single-celled organism, cyanobacteria, already existed on Earth. According to stellar evolution theory and the analysis of ancient rocks and meteoritic material, the formation of the Sun and Earth predates the appearance of these organisms by at least a billion years or more. It took approximately 5 billion years after the formation of the solar system from the primordial nebula for humans to appear on Earth. Furthermore, scientific investigations show that in the last 500 million years (based on fossil records), there have been five mass extinctions. Humans evolved from apes after the last extinction event 500 million years ago. Environmental changes in celestial bodies often determine the fate of many lives; for example, the extinction of dinosaurs 65 million years ago is said to be the result of a cold ice age or the impact of a small celestial body about ten kilometers in diameter.
Since the beginning of the 20th century, the achievements of astronomical research have been significant, including many discoveries about the Milky Way, extragalactic nebulae, and the expansion of the universe—particularly the later discoveries of quasars, interstellar molecules, pulsars, and extragalactic supernova explosions. Entering the era of space science and computer science, research into cosmic bodies has deepened, with many new celestial bodies discovered and explored every year.
Rational scientists are convinced that life is an inevitable result of the development of cosmic bodies under certain conditions. Scientists believe that life can only appear on planets around stars that emit light and heat, but not all stars have planets. According to the “nebular hypothesis” of the origin and evolution of the solar system, stars are formed from the contraction of a rotating primordial nebula. As it contracts, the rotation speeds up due to the conservation of angular momentum, and centrifugal force gradually flattens the nebula into a disk shape. When the central temperature reaches 7 million degrees, thermonuclear reactions converting hydrogen to helium occur, and a star is born. The material in the outer part of the disk condenses into several planets during the evolutionary process, while the remaining material forms dwarf planets, asteroids, comets, and other small bodies. Exploration of the solar system has shown that the natural conditions on Mercury, Venus, Jupiter, Saturn, Uranus, Neptune, as well as dwarf planets, asteroids, and comets, are harsh; none are suitable for terrestrial life.
The existence of life on Earth is truly marvelous; it is the proliferation of various forms of life that makes the earth vibrant and full of variety. Life is not created by gods but is the inevitable result of celestial evolution. The conditions for the emergence, survival, and development of humans are extremely demanding: first, the planet must have a solid rocky crust, a suitable atmosphere, and an appropriate temperature, along with a certain amount of liquid water; furthermore, the celestial body the planet orbits must be a stable star. In the solar system, Earth is located between Venus and Mars, neither too far nor too close to the Sun, right in the most favorable space for life to flourish. To date, no life has been found on Venus, Mars, or other planets. Computer simulations show that if there were no transfer of angular momentum during the contraction of the nebula, a central star and surrounding low-mass planets would not form; instead, a binary star system would be created. Even if planets formed in a binary system, they would soon fall into one of the stars or be ejected into space, making long-term existence around a star impossible. Therefore, a primordial nebula has at least two developmental possibilities: the material retains its original angular momentum and evolves into a binary star, or the two components part ways at just the right moment during evolution, resulting in a central star and orbiting planets.
A “Business Card” from Earth Sent into the Vast Universe
On March 2, 1972, and April 5, 1973, NASA launched the Pioneer 10 and 11 spacecraft. These were two small probes (with a mass of 259 kg) powered by nuclear batteries. They were the first “messengers” sent by humans beyond the solar system. They explored Jupiter and Saturn, respectively, and then passed Neptune. After completing their exploration missions, they flew into the vast interstellar space beyond the solar system, attempting to find human kindred spirits. Scientists estimate they left the solar system in the 1990s, never to return.
To allow extraterrestrials to understand Earth’s situation one day in the distant future, both spacecraft carry a “business card” of Earth—a gold-anodized aluminum plaque, 13.5 cm long, 7.5 cm wide, and 1.27 mm thick. The information on this “business card” was co-designed by Carl Sagan, Director of the Planetary Studies Laboratory at Cornell University, and Frank Drake, a famous astronomer and pioneer in the search for extraterrestrial intelligence (SETI), and was drawn by Sagan’s wife, the artist Linda Salzman Sagan.
On this aluminum plaque, a nude man and woman are depicted to show extraterrestrials the image of humans. The man has his right hand raised in a gesture of greeting. Behind them is a silhouette of the Pioneer spacecraft, scaled to the proportions of the humans. The designers believe that any extraterrestrial friends who intercept the spacecraft in the future will easily be able to estimate the height of humans based on this scale.
In the upper left corner of the plaque is a dumbbell-like pattern representing the structure of the hydrogen molecule, the most abundant substance in the universe known to humans. The circle drawn at the top left represents the orbit of an electron around the nucleus in a hydrogen atom; the markings at the center and on the circumference indicate the spin angular momentum directions of the electron and the nucleus. Since each hydrogen molecule consists of two hydrogen atoms, two circles are drawn on the card, connected by a horizontal line.
The center-left of the plaque uses direction lines from 14 pulsars to indicate the relative position of the solar system in cosmic space. The large circle at the bottom left edge of the card represents the Sun, and the third small circle to the right represents Earth. The curved line originating from here shows the departure route of the Pioneer spacecraft. The small circles represent Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (reclassified as a dwarf planet in 2006) according to their distance from the Sun, along with their relative distances. An arc is drawn from the third circle, showing the spacecraft flying outward between Jupiter and Saturn, thereby indicating the origin of the probe carrying this card.
This precious metal “business card” is extremely durable and will not change even after hundreds of millions or even billions of years. If one day Pioneer 10 or 11 truly encounters advanced intelligent life on an extraterrestrial planet, will the extraterrestrials be able to read this “business card”? Will they be able to find us?
The “Sounds of Earth” Record on the Voyager Spacecraft
In 1977, the “Project Ozma” reached its peak. That year, Professor Drake successfully persuaded NASA to include a gold-plated copper phonograph record on the Voyager planetary probes (bound for beyond the solar system). One side of the disc contains information about Earth, while the other side features popular and classical music. Voyager 1 and 2 were launched in August and September 1977, respectively. A few years later, after completing their interplanetary exploration missions, they left the solar system to become the second group of human “cosmic messengers.” Like “bottles in the cosmic ocean,” people hope they will encounter human “kindred spirits”—extraterrestrials—in the vastness of space.
The two spacecraft are identical in size and design, with a mass of 820 kg. On the side of each spacecraft, an aluminum box is secured with several precision bolts. Inside the box is a ceramic cartridge, a diamond stylus, and a gold-plated copper audio-visual record with a diameter of 30.5 cm. Instructions for using the record, expressed in scientific language, are engraved on the aluminum cover. This disc is a precious gift from Earth to extraterrestrial intelligent life, titled “The Sounds of Earth.” This record is of extremely high quality and is carefully protected within the aluminum box; combined with the high-vacuum environment of interstellar space, its estimated lifespan could reach 1 billion years.
“The Sounds of Earth” contains a Statement to Extraterrestrials signed by then-U.S. President Jimmy Carter:
This Voyager spacecraft was built by the United States of America. We are a community of 240 million human beings among the more than 4 billion who inhabit the planet Earth. We human beings are still divided into nation states, but these states are rapidly becoming a single global civilization.
We cast this message into the cosmos. It is likely to survive a billion years into our future, when our civilization is profoundly altered and the surface of the Earth may be vastly changed. Of the 200 billion stars in the Milky Way galaxy, some—perhaps many—may have inhabited planets and spacefaring civilizations. If one such civilization intercepts Voyager and can understand these recorded contents, here is our message:
This is a present from a small, distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.
Jimmy Carter
President of the United States of America
The White House, June 16, 1977
The content of “The Sounds of Earth” is extremely rich. The record begins with 116 images. Astronomical images include: a map of the solar system’s location, photos of Earth, parameters of the solar system and the solar spectrum, as well as photos of the Sun, Mercury, Mars, and Jupiter. The solar system location map is drawn using binary code, showing the relative positions of the Sun and certain pulsars, as well as the relative position between the Andromeda Galaxy and the solar system when Voyager departed Earth. The solar system parameter map consists of two photos, using numbers to indicate the diameter and mass of the Sun and its surrounding planets, their distances from the Sun, and their rotation periods. Additionally, there are charts and photos reflecting other sciences, involving mathematics, physics, chemistry, geology, and biology, including simple geometric shapes, mathematical definitions, chemical definitions, and definitions of physical units.
Images depicting humans, animals, reproduction, and evolution include: human anatomical diagrams, silhouettes of men and women, sex organs of both genders, the fusion of sperm and egg, fertilized egg cell division, the morphology and position of embryos and fetuses, childbirth, and a mother nursing an infant. There are also diagrams introducing the evolution of vertebrates from fish, frogs, birds, and deer to humans. Photos reflecting the work and life of people on Earth are also abundant. Famous architectural photos include the Great Wall of China, the United Nations Building, the Taj Mahal in India, the Golden Gate Bridge in San Francisco, and the Sydney Opera House in Australia. Other photos showing customs, scientific, and cultural achievements include: astronauts walking in space, airplanes, trains, large radio telescopes (instruments for receiving radio waves from celestial bodies, such as the Arecibo Observatory), the structure and recombination of DNA, high-power microscopes, and X-ray images of a human hand. The disc also includes: an illustration from Newton’s System of the World showing how to launch a cannonball into orbit; a sunset; a photo of Chinese people eating and playing a finger-guessing game (Chaiquan); a teacher teaching primary school students to write; a zoologist observing chimpanzees; a scientist looking through a microscope; and photos of many people visiting ancient animal remains. To give extraterrestrials a full understanding of human physical characteristics, some photos specifically mark the average height and weight of adults, children, and the elderly.
The 35 types of sounds on “The Sounds of Earth” are mostly natural and real, with a few being simulated (such as the sound of planets moving or the rumbling sound of a pulsar’s birth). The record includes the rumbling of a massive volcanic eruption, the terrifying sound of the 1971 Australian earthquake, earth-shattering thunder, the sound of wind and rain, and the sound of rushing water. The barking of a dog is quite notable. Additionally, there are the calls of elephants, the bleating of sheep, the roar of chimpanzees, birdsong, frog calls, and the chirping of crickets. Human sounds include breathing, kissing, footsteps, heartbeats, laughter, and the crying of a six-month-old baby. Furthermore, there are sounds of trains, ships, trucks, tractors, cars, and horse-drawn carriages.
The 12-minute recording of 35 natural sounds begins with a dizzying whirling sound representing the planets of the solar system orbiting; then comes a chronological sequence of sounds—first the roar of the primordial Earth; followed by the sound of heavy rain forming rivers, lakes, and seas; then the emergence of life, sounds from the cold winds of the Ice Age, including the sound of stones being struck in the Stone Age; this section ends with the cry of a newborn baby and recordings of human breathing and pulse.
The 27 world-famous musical pieces recorded on “The Sounds of Earth” represent different eras, regions, and ethnic groups on Earth. The expert music panel set a high standard, striving to present the most beautiful music on Earth to our “kindred spirits”—extraterrestrial intelligent life. The pieces include the first movement of Bach’s Brandenburg Concerto No. 2, full of enthusiastic and warm greetings; the fifth movement (Cavatina) of Beethoven’s String Quartet No. 13 in B-flat major (Op. 130), which expresses human suffering, longing, and ideals. There are also “New Guinea Men’s House,” “Wedding Song” from Peru, the Chinese Guqin piece “High Mountain and Flowing Water,” and the guitar piece “Dark Was the Night, Cold Was the Ground.”
This record, which carries humanity’s hope of finding extraterrestrial kindred spirits, showcases the vibrant environment of Earth alongside human loneliness. It is no easy task to tell extraterrestrials everything most representative of humanity from ancient times to the present in just two hours! The recorded statement by then-UN Secretary-General Kurt Waldheim says:
“As the Secretary-General of the United Nations, an organization of many states which represent almost all of the human inhabitants of the planet Earth, I send greetings on behalf of the people of our planet. We step out of our solar system into the universe seeking only peace and friendship, to teach if we are called upon, to be taught if we are fortunate. We know full well that our planet and all its inhabitants are but a small part of this immense universe that surrounds us and it is with humility and hope that we take this step.”
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