The origin of the solar system and the Earth
Man has always explored the planet Earth (the third planet in the solar system) to expand his knowledge and dreamed of exploring other planets.
A good place to observe the universe is the Observatory of Mauna Kei. The peaks rise proudly beyond the perennial cloud formations of Hawaii. From here perhaps it is possible to believe that one can see to infinity. Surely this is what scientists strive to do using the 8 huge radio telescopes installed here.
They provided us with extraordinary pictures of the universe. A close examination of the other planets helps us understand something about the miracle that is our planet.
At 4200 meters above sea level, the air is thin. Air movements are insignificant and do not alter the observation. Here we begin the exploration of the solar system, that contains other planets.
Saturn with its well-known rings: that belt around the planet may not be solid, but it is wide enough to accommodate five Earth planets in a row.
Jupiter is 900 times the size of Earth and takes 10 hours to rotate around its axis. Jupiter is the largest planet in the solar system, and its 4 major satellites are about the size of the moon.
The solar system's 9 planets revolve around the sun. In the outermost orbits: Neptune, Uranus, Saturn, Jupiter; in the innermost orbits: Mars, Earth, Venus, Mercury.
Immediately beyond the orbit of the Earth is the planet Mars. More than any other this is the planet that has inspired theories in favor of the existence of other life forms, but with an average temperature of -60 degrees it is probably a lifeless world. The surface of Mars, like that of the moon, is covered with craters.
Mercury, whose proximity to the sun makes it barely visible from Earth.
In spite of the romantic dream and science fiction imagination it seems that in the solar system life exists only on Earth. Those who have seen our planet from space compare it to an oasis in the desert: deep blue in color it floats against the backdrop of a sea of darkness. Blue oceans, green plains and white clouds, the Earth is the bearer of life.
But how did the Earth form and how did it develop?
During the past decades our knowledge of the universe has increased considerably. The formation of the Earth is the greatest mystery and cosmic events that man has long guessed are about to be clarified.
The search began in 1609, when Galileo Galilei first turned his rudimentary telescope toward the moon and discovered those shapes that we now know to be craters. The discovery was followed by the inevitable question, "How did they form? Are they volcanic craters or scars produced by falling meteorites?" For example, the Voyager revealed the existence of a huge crater on Min, one of Saturn's satellites, and on Enceladus, an ice-covered satellite. Scientists came to the conclusion that the origin of the craters is not volcanic, but the result of meteorites colliding with the planet's surface.
Collisions between celestial bodies are not uncommon and often result in a merge of the two bodies. Craters therefore give us information about a planet's accretion mechanism. We know, for example, that the surface of the moon, like that of Mercury is similar to the surface the planet had billion years ago. When we look at the moon today we can get a fairly accurate idea of what the Earth looked like immediately after its formation.
The formation of our planet began about 4.6 billion years ago when the universe was about 10 billion years old. We cannot be extremely precise about what happened about 4.5 billion years ago, but we have a fair amount of knowledge about it. The dust and gas scattered throughout the universe mixed, forming a spiral of gas at a very high temperature. At the center of the spiral the gas began to condense, began to burn, and the sun was formed.
Consequently, the gases began to cool, and just as steam produces water droplets, these gases began to condense. The result is what we call planetism. They were a huge amount, probably 100 trillion, each resembling an immense ball of coal about 10 kilometers in diameter. Perhaps it is not hard to imagine that they were beginning to collide with each other. Sometimes the planetesimals would fragment, sometimes they would stick together forming a larger body.
Such conditions continued for long times and finally a change intervened in the way the collisions occurred. Gradually a body much larger than the others appeared among the smaller planetesimals. The increase in its mass produces an increase in the force of attraction thus attracting more and more planetesimals. Collision with other bodies accelerated its growth.
This process continued by increasing the size of the new planetesimal at a faster and faster rate until the primordial Earth was formed. This is the same process to which Mercury, Venus and Mars grew. After its formation the Earth still bore with the marks of all those collisions. However, the process continued, always with greater intensity. In the first period the surface of our planet was covered with craters. One can get an idea of what it might have looked like by taking a look at the moon since its craters have remained the same since their formation.
After 4.6 billion years there is very little left of what the Earth looked like then, but by looking closely one can discover traces of those events. Artificial satellite observations confirm the existence of more than 100 craters on Earth's surface, a large number of them in Canada. Here, in the wild north of Quebec there are 15 craters of various sizes. This is an uninhabited desert place, except for caribou herds, inaccessible for most of the year. The craters in this area could give us valuable evidence to solve some of Earth's mysteries.
Sixty degrees north, beyond the forest boundary, the tundra and among the many lakes we discover some remarkably round ones. This is the new character of Quebec, one of the sharpest contoured lakes on Earth, measuring about three kilometers in diameter and almost a perfect circle. It lies in the center of a vast plain bordered by sheer walls. The lake is very deep, about 250 meters, is much deeper than other lakes in the area, the something explains its extraordinary color. When a lake is formed as a result of a meteorite colliding with the Earth usually the surrounding area continues to retain some fragments. But this crater is old and has passed through many ice ages, so that there is no trace of the meteorite left. We can only try to imagine the meteorite that produced this crater and the characteristics of the impact.
How much energy was required to generate a crater of this size? Knowing the amount of energy, we can calculate the speed of the body. It was probably between 15 and 25 kilometers per second. And assuming it was a rock meteorite with a density about 3,5 and 7 grams per cubic centimeter, we get a diameter of 100 to 300 meters.
A huge meteorite the size of a sports stadium crashes into the Earth at about fifty times the speed of sound. How colossal an impact of this magnitude must have been.
Laboratory experiment
Since the Apollo 11 exploration of the moon, NASA has continued its experiments on craters and their formation. When a meteorite hits the Earth it comes at a much higher speed than anything else moving on the surface. To simulate the collision we need very sophisticated equipment.
By shooting an aluminum projectile into a quantity of sand, we can get a crater.
The size obviously differs, but the resulting shape undoubtedly is that of a crater. These kinds of experiments are used to understand the process of crater formation. The impact takes place in a vacuum and is recorded with a high-speed camera. In an atmosphere like Earth's it would have looked very different. As the meteorite first advances at very high speed, it gains energy, becoming incandescent and brighter than the sun. Upon impact, the energy is released as heat, which evaporates the meteorite and surrounding rocks, producing a violent explosion. The shock wave is so powerful that sends the rocks into the air at supersonic speed. A mushroom-like column of molten rocks rises from the center of the explosion. The impact causes violent vibrations of the Earth. In less than ten seconds everything is over.
While craters on Mercury and the moon retain traces of the impact that produced them, on Earth, on the other hand, craters are eroded and eventually disappear, but despite this we can sometimes find evidence of a violent collision.
Here for example is the Barringer crater in Arizona
At 50,000 years old it is one of the newest craters on Earth. Faint traces of the collision that produced it can still be seen.
Upon impact, the surface opens up almost like a flower, while deeper layers, twisting, emerge outward. These layers are now visible along the rim of the crater. The body that hit the Earth had a diameter of about 30 meters and produced a 200 meters deep crater with a diameter of 12 kilometers. However, if we could transfer the Arizona crater to the moon, its size would be insignificant making it look like a grain of sand.
On the Earth, however, there are larger craters. What we now call Clear Water Lake in Quebec is one of them.
Clear Water lies in the middle of a desolate expanse dotted with numerous small lakes. It has a diameter of 35 kilometers and has right in the middle a ring of small islands. From space we can clearly see the circumference formed by the small islands, quite similar to other formations we have seen on the planet Mercury. Even on the moon there are craters with multiple edges like this one, the East Sea. It is 1,000 kilometers in diameter and its many rings appear to have been produced by a very violent impact.
Earth has also experienced impacts so violent that they have shaken the entire planet. In Quebec for example, there is the crater Manicouagan, which has a diameter of 65 kilometers. It is one of the largest on our planet. Satellite photos reveal the existence of a peak in the center of the crater. It bears a striking resemblance to the central peak that has been found in very large lunar craters.
When the impact is particularly violent, the crater floor actually experiences a backlash, and this produces a central peak. Could this be what happened in Canada? Today the crater is filled with water. There is a mountain ridge beyond the flat forest and lake area. This is the central peak, is 500 meters high and is composed entirely of rock. What kind of impact could this type of formation have produced? If we look at the rock we can see that it is quite reddish. This gives us evidence that it has been partly melted. The whole area must have been shaken violently at the time of impact such that it produced a peak like this almost instantaneously, which shows the amount of energy involved in the phenomenon. The rock in this area is similar to lava from a volcano. But how is that possible if there is no trace of a volcano in this area?
This rock was actually molten rock from the impact that formed a pond in the crater, then solidified as if it had been erupted from a volcano. Although it is similar to volcanic rock, its composition and position in the structure indicate that it originally melted after the impact.
This lunar crater was formed 280 million years ago by a strong collision. In its center we see a peak, all around it was red hot magma. This phenomenon must have repeated itself countless times on Earth, and at the time of our planet's formation these kinds of giant collisions must have been very frequent
The primordial Earth continued to grow and at the same time the craters increased in number. As the planet increased its mass it exerted an increasingly strong gravitational force, attracting larger and larger celestial bodies in ever greater numbers. The size of the impacts and their ability to melt the Earth's surface, such as the one that formed Manicugan crater, also increased.
The surface of the planet began to change. More conspicuous collisions caused the Earth's crust to melt. Magma, red and fiery, leaked out, covering the entire planet.
The melting point of the magma was 1,300 degrees, which is the temperature at which the Earth's surface melts, and it took a long time for the rocks to cool.
Thus our Earth born as a cold planet became a glowing ball transformed into an ocean of magma by successive collisions with other celestial bodies.
The magma ocean was 1,500 kilometers deep and the surface temperature was around 1,300 degrees. Meanwhile, other planetesimals kept colliding with this glowing planet. In them were contained the various elements of which the Earth is currently composed. As soon as the planetesimals collided with the Earth, the elements were instantly melted.
The formation of the oceans
How different the Earth looks today! 4 billion and 600 million years later, our planet is very different from today: atmosphere and oceans are not yet present.
How did the oceans emerge from the glowing ball that was the primordial Earth?
Analysis of meteorites has allowed us to understand something about their formation. Some of them contain the raw materials of our planet's formation and are still preserved exactly in their original state.
The museum in Mexico City for example is home to some of the largest meteorites in the world. This one, for example, weighs 22 tons. It is almost all pure iron.
But how was it formed? Scientists think it is a fragment of a growing celestial body. Once it reached a certain size, the heavier substances that made it up concentrated into a central iron core. A subsequent explosion destroyed the core and some fragments fell to Earth.
Of greater interest, however, are meteorites that have not undergone accretion since the original epochs. They currently roam the universe as they did billions of years ago at the time of Earth's formation. An examination of these meteorites will certainly give us a great deal of information about the raw materials that formed our planet. Sometimes these meteorites fall to Earth as in February 1969 in a small village in Mexico. The Allende meteorite, named after the place where it fell, brought this remote village to the attention of the scientific world. It happened in the period immediately before the launch of Apollo 11, when everyone's attention was on the space, but for the villagers the meteorite's arrival was a much more important event.
Some villagers still keep the fragments. To us may not look interesting, but to scientists it offers information going back more than 4.6 billion years, to the time when the solar system was created. This information could unlock many of the mysteries surrounding the accretion of the Earth.
How did it occur? What materials were present? The answers to these and other questions may lie in the fragments of the meteorite that hurtled through the night sky and fell on Allende.
Suddenly it seemed to be in broad daylight. The sheets and roofs of the houses vibrated, the metal windows rattled. When the light went out we heard a great noise: it was the falling stones; then we realized it was falling stones, we didn't know what that noise was so loud, it was the falling stones.
That strange phenomenon was the arrival of an interstellar messenger, a witness to the formation of our planet. The meteorite retains its original composition of hot gases from the primordial solar system cooled and solidified.
This is the Murchison meteorite that fell in Australia in 1969.
The fact that it also contains a large amount of water aroused considerable interest and excitement. Water thus existed in the solar system more than 4.5 billion years ago. It is therefore logical to assume that meteorites gave rise to the oceans on Earth. An examination of the water contained in meteorites could yield interesting results.
But how did the water get inside the meteorite? Scientists concluded that water steam became trapped in the solid substances when the solar system cooled.
Laboratory experiment
An experiment on fragments of the Murchison Meteorite was carried out in an analysis laboratory at the University of Tokyo.
The universe in which the meteorite wandered before it landed on the Earth was relatively cold. By heating it to 800 degrees, one should be able to release some of the water it contains. At the university researches crumble a sample of the meteorite into small pieces and heat them up. The glass of the container fogs up, the meteorite water begins to vaporize.
As the meteorites fell to Earth the water in them vaporized, condensed again and spread out forming oceans. During those billions of years the planetesimals continued to be drawn toward the ever-growing planet Earth shattering into the great ocean of magma. The substances began to separate and the heavier elements such as iron sank while the lighter ones remained on the surface.
Many of the planetesimals must have contained water, and much of this water vaporized at the same instant it touches the Earth.
In contrast to the iron that sank into the bowels of the Earth, water in the form of vapor rose upward. Together with other gases, including carbon dioxide, it formed thick clouds, and due to gravitational attraction these gases did not disperse into space-this was the beginning of the Earth's atmosphere.
It is very unlikely, of course, that similar changes did not also affect other planets, particularly Venus, Earth's sister, but while Earth can boast the presence of oceans, Venus is a completely dry planet. Why this profound difference? The clouds that surrounded both of these planets were subject to solar radiation that caused them to dissolve. On Venus the decomposition was rapid, the amount of vapor decreased very quickly until the planet was left completely waterless.
The same situation began to occur on Earth when the clouds succumbed to the relentless solar radiation. Had it not been for a strange twist of fate, the Earth would have remained uninhabitable. Fortunately, as soon as the number of planetesimals decreased, the ocean of magma began to cool, the temperature of the Earth began to fall. As the surface cooled, the temperature above the Earth's crust also fell. The thick clouds at about 500 kilometers began to lower.
The decisive turning point came when the Earth's surface temperature dropped to about 300 degrees. Torrents of rain fell on the surface of the still-boiling planet. The rain caused the temperature to drop even more, and this produced even more rain. This cycle continued for a long time until the planet's surface was completely flooded. The Earth was covered with oceans. Compared to the long process of evolution that began soon after, we could say that the formation of the seas happened instantaneously.
Finally the clouds opened and the first ray of sun shone on the newly formed oceans.
Without the oceans, without the incredible combination of circumstances that had produced them, the Earth would never have hosted life. Today there is not much left on Earth to remind us of its violent and sudden formation more than 4.5 billion years ago. Few things help us understand: among them the oldest known rock formation found at Isaiah in southwest Greenland. Its age is calculated to be around 3 the billions and 800 million years. In other words, it cooled and hardened about 800 million years after the birth of Earth.
This formation is accessible only during the short Arctic summer. The ice, which covers Greenland, is several thousand meters thick, and the oldest rock on Earth can only be seen in the summer.
This structure suggests that the rock managed to remain whole despite the distortion caused by the long period of exposure to the Earth's heat, meaning that the oldest rock on Earth probably formed under the sea.
As far as we know, the universe is essentially uninhabited, the only known exception being the Earth.
Our miraculous lifeless planet was transformed from the moment the oceans were formed; this was the beginning of its evolution. Today, planet Earth nurtures an infinite variety of living forms. It begins 4.6 billion years ago.
