Earth is a unique planet, and there are plenty of reasons for this. From the anthropic view, Earth is our home. From the scientific view, Earth is the only planet that supports life, and this happens because of the existence of liquid water on its surface and an atmosphere that allows life to flourish. Thanks to life’s presence, together with some peculiarities of our planet, there are many things that can be called “fun facts Earth”. In a nutshell, these are:
- Earth is the only planet that supports life as far as we know.
- The Earth’s rotation is gradually slowing.
- Earth’s rotation axis is tilted by 23 degrees. Thanks to this, we have seasons on our planet.
- Earth has a powerful magnetic field.
- The Earth is the densest planet in the Solar System.
- Earth has one natural satellite (the Moon) and five co-orbital satellites.
Earth is the only planet that supports life
Earth is the only planet (at least to our knowledge) that supports life. This makes our planet unique. Our planet has all necessary conditions for life support. These conditions cannot rank in importance, but let’s see what they are.
- Earth is a rocky planet – this means that Earth has a solid surface, where you can stand and walk. This cannot be possible on a gaseous planet like Jupiter.
- Earth has liquid water – water is one of the most important elements to support life, and it has to be in liquid form for this to happen.
- Earth has an atmosphere – more on the atmosphere below.
- Earth orbits the Sun at the right distance – Earth orbits our Sun at what we call the habitable zone. In every planetary system, there is a zone where it is prosperous for life existence, and Earth orbits at the ideal distance.
Formation of the Earth
Earth and the rest of the planets formed together with the Sun. The eldest detected material in the Solar system is 4.56 billion years old. Around 20 million years later, the primordial Earth formed. The Sun and planets formed from the gravitational collapse of a small part of a giant molecular cloud. Most of the mass accumulated at the center, forming the Sun, while the rest through flattening formed a disk around the proto-Sun. The small, dust and ice particles in the disk (known as proto-planetary disk), clumped together, forming bigger granules. This process lasted for a period of around 20 million years and led to the formation of the protoplanets.
Fun fact: The US astronaut Donald R. Pettit showed this accidentally while running experiments at the International Space Station. He put some salt crystals and water inside a bag. As you can see in the image below, granules started forming through clumping of the salt crystals.
Earth in numbers
Earth has a mean radius of 6371 km (the equatorial radius is 6378.1 km, and the polar radius is 6356.8 km). The shape of the Earth is nearly spherical, and the reason for the radius variation is its rotation.
Earth is the most massive rocky planet in our Solar system, and it orbits the Sun at a mean distance of 149,598,023 km (this distance is known as one Astronomical Unit, and it used to measure distances within our Solar system). The amount of time that the Earth needs to complete one orbit is equal to 365.256363004 days, or 1.00001742026 years (yes this is a bit longer than what we call a year, but this is true).
The mass of the Earth is 5.98×1024, and it has a mean density of 5.514 g/cm3, making it the densest planet in the Solar system. The gravitational acceleration at the surface of the Earth has a mean value of 9.81 m/s2.
The most abundant element on Earth is iron (32.1%), followed by oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulphur (2.9%), calcium (1.5%), and aluminum (1.4%). The remaining 1.2% is the abundance of the remaining elements. If you find these values strange, note that we humans experience only Earth’s surface. Earth’s core consists mostly of iron (90%) and nickel (5.8%), and it accounts for 30% of Earth’s mass.
The mean temperature at Earth’s surface is 14 °C (57°F). The temperature variation is significant with the maximum reaching 57°C (134.5°F), and the minimum -89.2°C (-128.6°F).
The oceans cover 71% of Earth’s surface, and only 29% is land. Oceans seem vast to us, but in terms of mass contribution on Earth’s mass, they contribute only 0.02%.
As a rocky planet, Earth is divided into three main layers. The outer layer of the Earth is the crust, the thinnest of the three. It consists mostly of silicate material and it has a variable thickness. This can be as little as 6 km under the oceans, to 30-50 km at the continents. The crust together with the upper and solid part of the mantle form the lithosphere. The latter is divided into what we call tectonic plates, which are responsible for the continental drift, which has reformed Earth over millions of years.
The mantle makes up about 84% of Earth’s volume. It is predominantly solid, but behaves as a very viscous fluid. Movements of material in the mantle affect the surface through the drifting of tectonic plates. At the upper mantle (which goes down to 660 km from the surface), the temperature varies between 500 to 900 °C (932 to 1,652 °F). The lower mantle lies between 660-2890 km, and the temperature in this region can exceed 4,000 °C (7,230 °F).
The outer core has a thickness of around 2300 km, it is in a liquid form, and it is believed that it is composed of 80% iron. The temperature of the outer core ranges from 4,030 °C (7,280 °F) in the outer regions to 5,400 °C (9,750 °F).
The inner core is composed mostly of iron and nickel and has a radius of 1,220 km. This is the densest region of the planet, thus elements like gold, platinum, and palladium are most likely present. The temperature here reaches 5,500 °C (9,930 °F), the matter is in solid form because of the high pressure which keeps metal from melting.
Fun facts: The upper part of the mantle and the crust, are responsible for all geological activity on our planet. These known as earthquakes, volcanoes and mountains and ridges.
Is the Earth slowing down?
Earth’s relative rotation to the Sun, also known as Solar day, is equal to 86,400 seconds or 24 hours. A sidereal day, Earth’s rotation with respect to the stars, is equal to 23hours 56 minutes and 4.1 seconds. The difference in the duration between a Solar day and the sidereal day may sound interesting, but the fact that Earth is slowing down outshines it. Earth’s rotation slows down by 2.3 milliseconds per century. We know that the gravitational interaction between the Moon and Earth causes the tides. The tides gradually stabilize the rotation of the Earth on its axis, thus making the planet slowing down.
Earth’s atmosphere, or what most of us call air, is a layer of gases that surrounds the planet and it is retained by Earth’s gravity. Earth’s atmosphere is our life-protector, since due to pressure liquid water exists, it warms the planet through the greenhouse effect, it reduces temperature extremes between day and night, and it also absorbs the ultraviolet radiation from the Sun. Our atmosphere comprises 78% nitrogen, 21% oxygen, 0.93% argon, with small amounts of other gases (carbon dioxide, helium, hydrogen). Air also contains water in vapor, and its abundance is around 0.4%. The layers that compose Earth’s atmosphere are:
- Troposphere: 0 to 12 km – Around three-quarters of the atmosphere’s mass are on this layer. All “weather activities” of the planet take place at this layer.
- Stratosphere: 12 to 50 km – The ozone layer, responsible for the absorption of the ultraviolet radiation from the Sun, is located at this layer.
- Mesosphere: 50 to 80 km
- Thermosphere: 80 to 700 km – Fun fact, if you build your own rocket and reach an altitude of 100 km, you are officially in space.
- Exosphere: 700 to 10,000 km – This is the outer layer of our atmosphere, which also interacts with the Solar wind (high energy charged particles emitted by the Sun).
Earth’s magnetic field
If you use a compass, you see that it points to the north, or to be more precisely to the magnetic north. This effect is due to the magnetic field of the Earth. The source of Earth’s magnetic field sits at its core. A dynamo process at the core converts the kinetic energy of the semi-fluid material into electrical and magnetic field energy. The field extends outwards towards the surface forming a dipole. By this point you would wonder if there are any fun facts about the magnetic field. There are actually, and these are:
- Earth’s magnetic field protects the atmosphere from the solar wind.
- The magnetic poles drift, causing field reversals. The most recent took place 700,000 years ago.
Earth, Moon, and five more?
Everyone knows that Earth has a natural satellite that orbits Earth, the Moon (Moon fun facts will be on the next article). But the Earth and Moon are not alone. We currently know that Earth has five quasi-satellites. These objects are a couple of hundreds of meters in diameter and they are Earth’s co-orbital followers.
We saw some interesting facts about our planet, which makes it unique. We need to understand that Earth is our home, and it is our duty to protect it. So the choice is ours, having a beautiful blue planet or something like Venus.