Earth is the third planet in order of distance from the Sun and the fifth largest in the Solar System in terms of both mass and diameter. Moreover, it is the only celestial object known to harbor life. It orbits the Sun in 365,256 solar days – a sidereal year – and rotates on itself relative to the Sun in 23 h 56 min 4 s – a sidereal day – that is, a little less than its 24 h solar day due to of this movement around the Soleila. The axis of rotation of the Earth has an inclination of 23 °, which causes the appearance of the seasons.
According to radiometric dating, the Earth formed 4.54 billion years ago. It has a single natural satellite, the Moon, which formed soon after. The gravitational interaction with its satellite creates the tides, stabilizes its axis of rotation and gradually reduces its speed of rotation. Life would have appeared in the oceans at least 3.5 billion years ago, which affected the atmosphere and the earth’s surface through the proliferation of organisms, first anaerobic and then, following the explosion Cambrian, aerobic. A combination of factors such as Earth’s distance from the Sun (about 150 million kilometers – an astronomical unit -), its atmosphere, its ozone layer, its magnetic field and its geological evolution have allowed life to evolve. and develop. During the evolutionary history of living things, biodiversity has experienced long periods of expansion occasionally punctuated by massive extinctions; about 99% of the species that once lived on Earth are now extinct. In 2020, more than 7.7 billion human beings live on Earth and depend on its biosphere and natural resources for their survival.
Earth is the densest planet in the Solar System as well as the largest and massive of the four terrestrial planets. Its rigid envelope – called the lithosphere – is divided into different tectonic plates that migrate a few centimeters per year. About 71% of the planet’s surface is covered by water – notably oceans, but also lakes and rivers, constituting the hydrosphere – and the remaining 29% are continents and islands. Most of the polar regions are covered with ice, especially with the Antarctic Ice Sheet and the Arctic Ocean pack ice. The internal structure of the Earth is geologically active, the solid internal core and the liquid external nucleus (both composed mainly of iron) making it possible in particular to generate the Earth’s magnetic field by dynamo effect and the convection of the Earth’s mantle (composed of silicate rocks) being the cause of plate tectonics.
The origin of the Earth
Before Earth appeared, dust floated in space that aggregated and formed the solar system and its planets. This dust came from other stars at the end of their life which exploded. Iron, carbon, uranium, gold, hydrogen, helium: all these elements are at the origin of the formation of the planets and the Earth. The dust grains gathered to form a mass which gradually grew in space. As they grew in size, the gravity of these rock-turned objects also increased, attracting more and more rock.
Over four billion years ago, hell reigned on Earth. Millions of asteroids and comets were constantly hitting it. At that time, the Moon was much closer to the Earth than it is today. The sunlight was much weaker. As for water, it did not exist. The Earth was covered with volcanoes spitting their fire with unimaginable fury. Toxic gases continuously escaped from these volcanoes, contaminating the primitive atmosphere. One wonders how such a hostile world could have given birth to this profusion of life that we know today …
The Earth is over 4.5 billion years old, a number that is beyond belief. To better understand time on this scale, we often take the example of the clock: if we reduce the 4.5 billion years to a period of 24 hours, we obtain a result which shows that man is on Earth for a very short time.
The clock example shows that the first single-celled organisms appear around four in the morning. The first multicellular organisms land at 9:05 p.m. The dinosaurs appear around 10:50 p.m. As for the first humans, they barely arrive thirty seconds before midnight!
When we consider that dinosaurs ruled the Earth for about 150 million years, modern man looks very pale with his 150,000 years!
Clock of life
It is very difficult, if not impossible to calculate the exact age of the Earth, because it has been a long time since the traces that could have testified to its formation disappeared. The only way scientists can calculate this age is to study other objects available in the solar system.
The asteroid belt between Mars and Jupiter contains countless rock objects, many of which came from the formation of the solar system. By studying such pebbles, it is possible to get a good idea of the age of the Earth. Some of these asteroids regularly collide and are deviated from their path. About forty thousand tons of these objects crash into Earth every year!
Most disintegrate on re-entering the atmosphere, but the larger ones (some can weigh up to 200 kg) sometimes manage to crash into Earth. A real boon for researchers, because by studying such pieces of rock from the depths of space, it is possible to find clues to the origin of our planet.
Some meteorites found in icy lakes have retained much of their chemical properties, the same as the first grains of dust that formed the Earth more than 4.5 billion years ago! To define the age of the Earth, scientists use a method of radiometric dating on objects found on Earth. Each time, these objects are approximately 4 billion and 550 million years old, which gives a good estimate of the age of our planet.
The earth’s atmosphere changes continuously into space, so that it is not sharply delimited at the top. Their mass is about 5.13 × 10 18 kg and thus makes up almost one millionth of the earth’s mass. In the atmosphere at sea level, the mean air pressure under standard conditions is 1013.25 hPa.
The atmosphere on the ground consists mainly of 78% by volume nitrogen, 21% by volume oxygen and 1% by volume noble gases , predominantly argon . In addition, there is 0.4% by volume of water vapor in the entire earth’s atmosphere. The one for the greenhouse effectThe important proportion of carbon dioxide has increased due to human influence and is currently around 0.04% by volume.
|101.325 kPa (at MSL)
|Composition by volume
|6371.0 km (3958.8 mi)
|6378.137 km (3963.191 mi)
|6356.752 km (3949.903 mi)
|1.08321×1012 km3 (2.59876×1011 cu mi)
|5.97237×1024 kg (1.31668×1025 lb)
|5.514 g/cm3 (0.1992 lb/cu in)
|9.80665 m/s2 (1 g; 32.1740 ft/s2)
Moment of inertia factor
|11.186 km/s (40270 km/h; 25020 mph)
Sidereal rotation period
(23h 56m 4.100s)
Equatorial rotation velocity
(1674.4 km/h; 1040.4 mph)
The internal structure of the Earth
The internal structure of the Earth refers to the distribution of the interior of the Earth into nested envelopes: mainly the earth’s crust, mantle and core, according to the current geological model, which attempts to describe their properties and behaviors during geological times.
These layers are delimited by discontinuities, which can be identified using seismology. This made it possible to determine the state of matter at inaccessible depths.
This constitution can be understood by going back to the formation of the Earth by accretion of planetesimals, of which the primitive meteorites, or chondrites, constitute the memory. The different layers were then put more or less gradually in place under the influence of various physical parameters, such as the density and the rheology of the various phases constituting the raw materials, as well as the chemical affinities of the elements for the various mineral phases, c that is, chemical differentiation.
The outer core
The outer core is the liquid part of the Earth’s core, an intermediate layer located above the solid seed (inner core) and below the Earth’s mantle. Like the seed, the core is a metal alloy, mainly made up of iron and nickel. The liquid of the outer core is animated by rapid convective movements which induce a dynamo effect at the origin of the Earth’s magnetic field.
How fast is the Earth moving in space?
The speed of the Earth? We do not feel it but yet the Earth turns on itself. Thus, a point located at the equator travels some 1,670 km (1037.69 miles) per hour!
We don’t feel the Earth spinning, but that doesn’t prevent objects on its surface from betraying its movement. Indeed, the rotation of the Earth is responsible for a Coriolis force which deflects inertial movements to the right in the northern hemisphere and to the left in the southern hemisphere.
THE EARTH TURNS ON ITSELF (ON ITS AXIS)
You don’t have your head spinning, and yet our blue planet rotates on itself every second. At the equator, the speed of rotation is 1,600 kilometers per hour, or 40,000 kilometers per day. The Earth’s equator, not to be confused with the country of South America, is an imaginary line in the center of the Earth. It marks the separation between the northern hemisphere and the southern hemisphere. We the French are moving at around 1,100 kilometers per hour or 317.4 meters / s. Finally, our Earth friends from the North Pole and the South Pole turn at only 3 kilometers per hour. Today, know that our planet spins more slowly than it did several million years ago.
EARTH SPINS AROUND THE SUN
Imagine a fun fair merry-go-round with your family seated in the seats of a small capsule. This turns on itself, then begins to rotate with the other capsules of the merry-go-round around a central axis. It is in fact the same pattern for Earth and the other planets in the Solar System.
In a year there are four seasons. Summer and spring when the Sun is stronger and more present, then winter and autumn with nights longer than days. These changes are due to the path of the Earth around the Sun. Our planet takes 365 days to make 940 million kilometers, that is to say, the complete turn around the famous yellow star. We therefore travel with it, 107,000 kilometers per hour, or 29.8 kilometers per second.
HOW CAN WE BE SURE THE EARTH IS TURNING?
Scientists and astronauts are sure that for hundreds of years they have been studying precisely the movements of the Solar System and especially of the Earth. So that your little scientists can also become experts, three techniques: observe the sky as a family at night, the stars move, which proves that the Earth is spinning. You can also go see the famous Foucault Pendulum from the church in Saint-Martin-des-Champs. It makes it possible to highlight the rotation of the Earth on itself by terrestrial means only. Finally, a little simple experiment to do with your children: the strength of Coriolis force. It shows the rotational motion of air and water similar to the formation of hurricanes.
Earth’s magnetic field
While Earth was still a rocky sphere, and volcanoes raged there, the planet’s gravitational force pulled enormous amounts of celestial debris, and radioactive elements warmed it from within. This whole process has caused a considerable increase in the temperature at the surface. The Earth is then just a ball of molten magma, almost entirely liquid. Iron began to melt and then flow into the interior of the planet, along with all the other denser elements, eventually creating a core of liquid iron in the center of the Earth. Other elements such as water and carbon rose to the surface. From this core is born a primordial invisible force which will be our shield: the terrestrial magnetic field.
Thanks to this core, the Earth becomes a giant magnet with two magnetic poles, north and south. Without this liquid core created in the early Earth, we would never have had an atmosphere, and life would never have appeared! Life in space is impossible, because solar radiation is far more dangerous than radiation from a nuclear explosion.
Thanks to the earth’s magnetic field, the trajectory of particles emitted by the solar wind is permanently deflected, and our planet and the life on it are protected. Without its core, the Earth would be like Mercury, a sterile sphere without life and without an atmosphere. Even the surface of Mars, which has a thin atmosphere, was scorched by the solar wind, as its core solidified and its magnetic field disappeared.
The Moon, our companion in space
During the Apollo missions in the early 1970s, scientists hoped that by analyzing chunks of moon rock, they would be able to find clues to the origin of Earth. When the lunar rocks returned to Earth, their dating was very astonishing: the Moon was younger than the Earth!
The theory on the formation of the Moon indicates that a few thousand years after the appearance of the Earth, a planet the size of Mars (named Theia), came to strike the Earth. The two planets merged to form one, and the debris began to spin around the Earth to eventually form the Moon.
Initially, the Moon was much closer to the Earth, and an Earth day lasted only five or six hours. The proximity of the Moon exerted an immense force of attraction on the surface of the Earth. This force literally swelled the earth’s surface by several tens of meters, which ended up slowing the speed of our planet’s rotation. The Moon is moving further and further away from us, and it continues to move away today. Measurements taken with a reflector placed on the Moon during an Apollo mission showed that the Moon moves away from Earth by 6 centimeters per year. Even though this remoteness may seem trivial given the size of the Earth and the Moon, this remoteness will indeed have an impact over the next millions of years.
The Moon’s rotation around the Earth allows it to maintain a stable axis. If the Moon were not there, our planet would oscillate in an erratic way, preventing the appearance of non-primitive life, due to sudden climatic variations.
Water from space
The presence of water on earth is the subject of several theories as to its origin. Previously, most scientists believed that water appeared in abundance on Earth about a billion years after it was formed. But new geological studies have shown that water appeared long before: just 200 million years after our planet was formed.
The condensation of water caused by the cooling of the earth’s crust is probably the cause of the formation of lakes and oceans. Water is essential for the proliferation of life as we know it on Earth. But how did all this water, which now covers 70% of our planet, get?
A large amount of water vapor has escaped from the roaring volcanoes long ago. But scientists agree that it is not enough for such quantities to be dumped on the planet, especially in such a short time.
One of the theories accepted by the scientific body is that most of the water present on our planet is extraterrestrial: it comes from space, most likely from comets that once bombarded the Earth, for millions. years. Half the mass of comets is ice water. A single comet such as Hale-Bopp (visible to the naked eye in 1997) contains enough water to fill 10% of the American Great Lakes, which is a lot for a single celestial object.
The theory explains that when it crashed into Earth, the ice contained in the comets would have turned into water vapor that would have covered the terrestrial expanses in the form of thick clouds. For millions of years, these clouds would have rained on the entire planet without stopping, creating the oceans, and turning the Earth into a blue planet.
However, there is a problem with this theory. The water in our oceans has too little deuterium (the isotope of the hydrogen atom) to come only from comets, which contain this element in large quantities. Scientists are still divided today on the true origin of the water, which probably comes from different sources (meteorites, comets, degassing …).
The origin of life
Although no one can say whether there was life 4.3 billion years ago, it can be said that the conditions were right for it. One of our great discoveries is the fossilized stromatolites (domed structures composed of microscopic bacteria), dating back more than 3 billion years, which bear witness to the emergence of life in ancient times. And today, it still exists in parts of the world like Australia. Stromatolites have created a world conducive to the emergence of life.
Billions of years later, life abounds in an incredible diversity of flora and fauna. This early microbial life form still exists on Earth, which manages to survive in extremely hostile conditions. Many scientists study these life forms in these hostile environments and compare them to the extreme environments of other planets and moons in the solar system, always looking for the same answer to this big question: does life exist in other worlds? ?
The first bacteria
Many researchers wonder how the first bacteria grew, divided, and began to reproduce. As if by a miracle, on young Earth, carbon molecules began to reproduce. One wonders what made these molecules create copies of themselves and turn into living cells. This is perhaps the greatest mystery of all time …
Astrobiologists have successfully demonstrated that the components of life proliferate in space and constantly fall on our planet in the form of microparticles. In order to study these particles of life and not to contaminate them, scientists send planes into the sky, at the edge of space, which collect these particles on their wings. Analysis of these particles revealed that they are rich in organic matter (amino acids) and are over 4 billion years old. In other words, life is an element that abounds in the universe!
Many researchers believe that the millions of meteorites that struck early Earth contained these amino acids, and it was through these amino acids that life began to flourish.
The great mutation of the Earth
At the end of the great meteor bombardment, when the debris has become scarcer in space, an incredible mutation begins on Earth. Microbial life begins to come out of its hiding places and to develop everywhere.
The sun will provide these bacteria with the energy they need to live and thrive. This is how chlorophyll appears. This green pigment absorbs energy from the sun through photosynthesis, and converts carbon dioxide into carbohydrate. As the Earth cools, it allows this new form of life to spread throughout the oceans, resulting in the biggest mutation in the history of our planet!
By absorbing carbon dioxide from the atmosphere, these bacteria release oxygen, which eventually accumulates in the atmosphere. Without these famous bacteria, there would be no oxygen in the atmosphere, and our planet would still be filled with poisonous gas. Without the existence of these primitive bacteria, there would be no plants or animals on Earth, and man would never have seen the light of day!
Oxygen doesn’t just help us breathe – it’s an element that protects us from the sun’s ultraviolet rays, along with the ozone layer. This layer protects us by filtering out harmful radiation, like sunscreen on the skin.
The evolution of life on Earth has only been possible through the hard work of bacteria that have oxygenated the Earth for more than three billion years…
Chemical composition of the crust[
Astrology: The element Earth is associated with the astrological signs Taurus, Virgo and Capricorn
The Earth element brings realism, something concrete. It is the ground, the solidity, the stability as well. But through this element we also find notions of rigidity, hardness, lack of flexibility. This element is feminine and indicates rather receptive and introverted personalities.
Earth signs certainly have an assertive character, but they shine above all with their realistic, down-to-earth side, one might say. Calm by nature, they like to move forward methodically, without haste. These are signs that are also distinguished by their materialism, their need for comfort. Without these aspects in their life, they can feel insecure.
Their work force is important and they know how to organize themselves to achieve their objectives. We appreciate them as collaborators for their thoroughness, their desire to do well and their pugnacity. We can sometimes blame them for lacking a little imagination and having too Cartesian mind. Which can make them pass, in certain circumstances, for poopers.
In all areas of their existence, they need stability and a minimum of tranquility. In love, they like to give and receive, seek sensuality, beauty and show themselves faithful to their partner. They hope to be able to build a home, a cozy little nest where everyone will evolve in a serene and reassuring atmosphere.
The association of the Earth signs with the Fire signs is interesting. If we allow ourselves a comparison with a chimney fire, the Earth signs are the hearth allowing the fire to take but while containing it, preventing it from spreading dangerously. So the Earth signs will find the warmth and enthusiasm they need while offering their partner a form of channeling their sometimes excessive energy…
With Air signs, the risks of disharmony are real. Certainly they can be found in the field of aesthetics but is this enough to consider a long-term relationship? Air signs, having difficulty in formulating their feelings, will not provide the security that Virgo, Taurus and Capricorn need.
Photo explanations: The solar system’s two outermost gas giant planets are compared with the Earth in this photo montage. Prepared for NASA by Stephen Paul Meszaros.