Genesis as told by science part II
Part two of the journey of existence. In this part I will talk about the formation of the solar system and our beloved Earth.
So, now that we know how the Universe came to be, and how it functions, its time to talk about how our solar system was formed; The Sun, the planets and Earth.
The the solar system took many shapes in our imagination, from ancient civilizations imagining a flat earth under a flat sky lifted without pillars, to classical Greece, drawing from naked eye observation a geocentric model of the Universe where a spherical earth lies at the center with all the celestial bodies orbiting it. The most prominent geocentric model was the Ptolemaic model; a spherical earth in the center of seven spherical heavens, each one of them occupied by a celestial body; The Moon, Mercury, Venus, The Sun, up until the heaven which contains the stars. It remained the most accepted model all over the world until the 17th century when it was gradually replaced by the heliocentric model where the Sun lies at the center of the solar system. However, the geocentric model maintained some of its fans rooting for it so far until 1985 in Saudi Arabia!!!!!! You can imagine me face palming now.
How this heliocentric model came to be is the topic of this article. The story of our dear solar system began 9 billion years after the Big Bang, when a nebula (gas cloud consisting mostly of hydrogen, almost more than 98%) started collapsing due to the gravitational force, and matter started accumulating in the center. As the nebula continues to collapse it spun faster and faster, as a figure ice skater when pulls his/her arms inwards. Matter got condensed causing atoms to collide generating more and more heat. The center, where matter is most concentrated became increasingly hotter. In the course of the next 100,000 years the nebula flattened just like a spinning pizza dough, with a protosun in its center (hydrogen fusion didn't yet begin)
Protoplanetary spinning discs started forming from the leftovers of the Sun’s formation. Why spinning discs you say? because of something called the preservation of angular momentum, don’t worry about it, its a nature’s prerogative, and that is why all the planets revolve around the Sun in the same direction, counterclockwise. Inside those discs, lumps of dust start clumping, with time getting bigger and bigger as they sweep materials, just like a snow ball. Slowly over millions of years forming larger bodies, eventually turning into the planets we all love.
Two groups of planets are formed, rocky terrestrial inner planets (Mercury, Venus, Earth and Mars) and gigantic gassy outer planets (Jupiter, Saturn, Uranus and Neptune) The inner planets are rocky because they were formed closer to the Sun where it is so hot only metals with high melting points are allowed to form. Those compounds are quite rare in the universe, comprising only 0.6% of the mass of the nursery nebula. Hence, the terrestrial planets couldn't grow very large. The giant gas planets were formed in the colder far regions, which allowed more volatile elements to remain in an icy form. Those elements were more abundant than the metals and silicates that formed the terrestrial planets, allowing the gas planets to grow massive enough to capture hydrogen and helium.
As the protosun got hotter, it reached a critical temperature and pressure, kicking start the hydrogen fusion, causing the Sun to ignite resulting in a shock wave called T Tauri Wind (so star treky) it is strong enough to blow away the left over ice, dust and gas from the inner planets, leaving them for the outer planets to capture. The reason why Jupiter, or Uranus for example didn't ignite into stars even though they are formed mostly of hydrogen and helium is that they didn't reach the critical mass to fuse hydrogen.
4.5 billion years ago, the Earth emerged from its nursery disc. It was a hot ball of molten lava spinning and orbiting the newly formed Sun. It was hot enough to melt the heavy metals. Having higher densities, those metals sank creating Earth’s iron core, which in turn created Earth’s magnetic field.
Over the next 500 million years, the Earth started cooling, solidifying its crust creating the first continents. Asteroids bombarded early Earth heavily introducing water into the atmosphere (water is so abundant in the Universe, also in the asteroids belts) As the planet cooled, clouds are formed. The atmosphere at that time was mainly carbon dioxide and methane producing greenhouse effect allowing liquid water to form thus the oceans.
Around 4 billion years ago, first life has emerged. Out of chemical reactions, the first self replicating molecules were synthesized, the transition from chemistry to biology. All models which attempt to explain this transition are hypothesis, none of them has been promoted to a theory. Meaning, still no one has a definitive answer to the problem of the origin of life.
In the next part, I will talk about the evolution of life from the first bacteria to the first human lineage.
