Wait But Why is a really cool blog. The blog is added to the Blog Roll. Fermi Paradox is an article that tries to explain why we do not receive communication from other civilizations in our galaxy. Based on Fermi calculations, there should be 100,000 intelligent civilizations in our galaxy. Though we have detected cosmic radiation from Big Bang (which happened 13.7 billion years ago), we have not detected radiations from other life forms. Is intelligence a rare phenomenon?
Combined Array for Research in Millimeter-wave Astronomy (CARMA)
For intelligent life to evolve on a planet, the planet should have several characteristics:
- Right surface temperature.
- Existence of carbon.
- Existence of water.
- Moving continents.
- Greenhouse gases.
- Right atmospheric pressure.
- Magnetic pole.
- Pass survival characteristics through DNA.
- Sense light with eyes.
- Measure time.
- Medium sized Sun.
- Moon to stabilise climate.
- Jupiter like planet in outer orbit.
- Catastrophe to kickstart evolution.
Right surface temperature
The temperature on the planet should be just about right. This can happen if the planet is within a certain distance from the star, also called Goldilocks zone. In the solar system, only three planets are within the Goldilocks zone – Venus, Earth, Mars.
Existence of carbon
Carbon binds with atoms like Nitrogen, Oxygen, Hydrogen to form long chains of molecules which is the foundation of life. For carbon to exist in a planet, the planet should be part of a second-generation star (a star that is formed by the remains of super-nova). Nuclear fusion happens in the star. Hydrogen fuses together to form Helium. The mass lost in the fusion process is converted to energy. When a first generation star dies, it has run out of hydrogen supply and is full of Helium. When Helium collapses under gravitational pressure, the temperature is high enough for Helium to fuse together to form Carbon. When the second-generation star dies (as a result of most Helium converted to Carbon), a super-nova usually happens that releases the carbon into space.
Existence of water
Apart from carbon, water is also essential for life to originate. Primitive life forms like bacteria started in the oceans. Such bacteria break down water and carbon-di-oxide with the help of sunlight to create their food. (photosynthesis). Stromatolites were responsible for releasing oxygen into the atmosphere for higher life forms to exist.
For higher life forms to exist, there should be land. The earth is divided into seven continental plates which move at the rate of 2 centimetre / year. When two continental plates collide, they create mountains or uneven surface on the earth. Without an uneven surface, the whole of earth will be submerged in water (oceans).
Earth’s atmosphere is about 100 kilometres thick. The earth is massive enough to hold the atmosphere by its gravitational pull. Mars had an atmosphere in the past and had a watery surface with regular rains. Mars has a weak gravitational pull, causing the atmosphere to completely escape. Without an atmosphere, Mars is a cold frozen planet with no possibility of life.
A thick atmosphere also protects the Earth from meteorites. With a thick atmosphere, most of the meteorites burn up by the time they reach the earth’s surface. Without the atmosphere, the earth will be bombarded by meteorites which will wipe out an entire city.
The planet should learn to maintain the right amount of greenhouse gases in the atmosphere. Greenhouse gases trap the energy from the sun and keep the planet warm. Without greenhouse gases in the atmosphere, the entire planet will freeze. Greenhouse gases are gases like carbon-di-oxide and methane. No greenhouse gases will cause the planet to freeze.
Right atmospheric pressure
The atmospheric pressure on the planet should be just right. If the planet has too much of atmosphere like Venus (100 times the earth’s pressure), the atmospheric pressure will snuff out life on the planet. If the planet has too less atmosphere like Mars, the liquid on the surface will vaporize. For example, the boiling point of water in Mt. Everest is 71 C (atmospheric pressure 0.34 times at the surface of earth). For more information, please read Armstrong limit.
The planet should have a magnetic pole. The magnetic pole protects the planet from cosmic radiation which will otherwise energize atmospheric gases and causes it to escape the planet’s gravitational pull. A planet can have a magnetic pole if it has a solid inner core, followed by a liquid outer core. The liquid outer core moves around the solid inner core. Since the core is made of iron, the movement cause a dynamo effect, creating the earth’s magnetic pole.
We still do not know how life on earth developed DNA. But what we know is, DNA is a helix made up of 3 billion protein molecules. Every cell in our body contains the DNA helix. When a cell replicates, as part of normal growth, the DNA is replicated with a very high accuracy (one in billion). DNA encodes all the characteristics of the life form. DNA preserves intelligence over time.
Sense light with eyes
Light are photons that travel from the sun which travel at 300,000 km/s. Colors are frequencies of the light. Our ability to sense light within a certain frequency was developed 400 million years ago. This led to an exponential growth of life on earth. (An example of a life form which cannot sense light is a tree).
Time is the ability to understand the passage of events. As humans, we sense time through various recorded events. We accurately measure time. We understand how the space-time universe works in the form of General Relativity.
The Sun is medium-sized. If the Sun was too large, then it will burn up fuel too quickly. It took 4 billion years for complex life to evolve on Earth. With a large sun, the planet will not have enough time for complex life to evolve.
Moon to stabilise climate
Earth is fortunate to have a large moon orbiting very close to Earth. The moons of other planets are smaller compared to the size of the planet and much farther from the planet itself. Since, the moon is close enough to Earth, it influences the climate of Earth. Without moon, Earth will experience wild climate fluctuations. In addition, ocean tides are a result of Moon’s gravitational pull. Ocean tides provided early life forms an opportunity to move from oceans to land.
Jupiter like planet
Earth is fortunate to have Jupiter revolving in an outer orbit. Jupiter is 300 times the size of Earth. It exerts a huge gravitational pull on comets. This shields Earth from dangerous comets which will otherwise strike Earth every 10,000 years. Every such comet strike will wipe out most of the life on Earth.
Catastrophe to kickstart evolution
If Earth was too stable, then there would be no evolution. Stromatolites are bacterial colonies which once inhabited all of earth. About 700 millions back, a gigantic ice age covered all of planet earth (Snowball Earth), causing most of stromatolites to disappear. Massive volcanic eruptions cleared the earth of ice age. After the ice age, earth had space for more complex life forms. The ending of Snowball Earth coincides with the Cambrian era of evolution, the era when species evolved eyes to sense light.
250 million years ago, the currents that distribute oxygen and nutrients in the ocean stopped. As a result, most of oceanic life became extinct. When the oceans became stagnant, they started releasing toxic hydrogen sulphide in the atmosphere causing most of land animals to become extinct. When the ocean currents stopped working, 90% of all life became extinct. The mass extinction, also called Permian-Triassic extinction, paved the way for dinosaurs.
Dinosaurs dominated the earth for over 200 million years. 65 million years ago, a 30 metre meteor struck Mexico (Chicxulub crater) causing most of dinosaurs to become extinct. This paved the way for mammals to evolve in earth. If mammals did not evolve, we would not be here.
Earth is resilient and has recovered from each global catastrophe. The global warming that humans are creating is triggering another massive extinction. Though the Earth may survive, the human race may not survive, as we are destroying the very conditions that ensured our survival.
We are intelligent life forms. But, we are not alone in the universe. Most of the arguments in the article come from the Rare Earth hypothesis. But, there are some scientists who believe that such conditions may not be rare.
According to such scientists, for every earth-like planet, the probability of intelligent life evolving on the planet is quite high, approximately 0.22. And so, there should be 100,000 civilizations (like us) in our galaxy. Yet, we have not received any communication from other intelligent life forms. This is called Fermi Paradox. The article from What but Why provides alternate explanations about why this is the case.