How Did the Solar System Form? How Did Life Form?

Formation of the Solar System

The accepted theory concerning the formation of our solar system, ‘nebular theory,’ conveys that our solar system originated as a solar nebula with hydrogen that later condensed into the protosun – protosun derives from protostar, which is a star still gathering mass from the surrounding molecular cloud. Rocks, gasses and other debris contained within the gravitational pull of the protosun condensed with other objects to begin forming the objects presently revolving around the sun, like planets and asteroids.

The earth formed as one of these large rocks whose superior gravitational pull resulted in collisions with many smaller rocks. The chaotic early solar system was packed with asteroids, comets, and even small protoplanets, many of which collided with our planet. 

One example was the Theia impact, also known as the Big Splash, a hypothetical collision between earth and a protoplanet that resulted in large amounts of earth being launched into orbit around the planet; the ejected material began to materialize into greater chunks, forming rings (yes, rings) around the young planet. The rings would later condense into our moon. The facts that the moon is very iron-poor (it is extremely unlikely that Theia could’ve penetrated to Earth’s core, which is where a majority of the iron is), that the major collision would explain young Earth’s insanely rapid rotation (which had been around 6 times as fast as it does now), and that the absence of volatile elements on the moon because volatile elements launched into orbit would’ve been vaporized due to the energy released in the event, support the Theia impact hypothesis. 

Early Evolution of Earth – Plus the Formation of Life

Earth’s first days were incomprehensibly hellish. The early solar system was littered with debris oribiting the young earth and colliding with it. The collisions resulted in a gradual increase in Earth’s size, known as accretion. It is believed to have taken around 100 million years for earth to grow (or “accrete”) to near its present size.

As the collisions decreased, so did earth’s temperature decrease. Volcanic eruptions soon became the source of a new atmosphere on earth; this atmosphere was composed mainly of methane, hydrogen, sulfide, and carbon dioxide. A few hundred million years later (around 500 million after earth’s formation), water began to pool on the surface.

 Not too long after water began to pool, the first life is believed to have formed (this would have been around 3.9 billion years ago). Life on earth could be as old as 4.1 billion years old, but we have only discovered fossils of ancient organisms as old as 3.7 billion years. 

The earliest evidence of life came from the remains of an organism called a stromatolite, the fossils of which are around 3.7 billion years old. While scientists generally agree on the time in which life formed, there remains a limited understanding of how it formed (how life formed is easily one of humanity’s most plaguing questions). 

While we do not know exactly how life formed, we do have hypotheses that could possibly explain life’s origins. 

The first of these hypotheses is the RNA World Hypothesis, which conveys that life on earth originated from the formation of RNA on Earth. The hypothesis is supported by the fact that the genomes of early organisms were likely composed of RNA, not DNA. The RNA World Hypothesis, however, does not explain how the RNA itself arose (so, like most hypotheses that deal with a sort of genesis, the hypothesis does not sufficiently trace all the way back to the beginnings – to the creation of nucleic acids and, thus, RNA, themselves).

The second of these hypotheses is considered the anthropic principle. This hypothesis was floated by Richard Dawkins, but it also does not explain how life may have formed on Earth. The anthropic principle states that because there are, conservatively, at least a billion billion planets in the observable universe it is likely that life would form on at least one of these planets. Beyond even a billion billion planets, a multiverse with many universes containing a billion billion planets could make the existence of life probable, if not inevitable. This hypothesis again does not explain the origin of life on Earth, but it does hint at the likelihood that life can form on at least one planet – that one planet being ours, of course.

The last hypothesis is the most accepted in the scientific community. The proposed event is called abiogenesis – essentially, extremely simple life arose from dead-matter, which bonded to form biomacromolecules and RNA/DNA, leading to the genesis of microscopic, simple organisms. Biogenesis (the process of reproduction produces new life) soon replaced abiogenesis to be the new form in which life would form. Abiogenesis, indeed, makes logical sense, especially considering all of the primary elements composing a vast majority of the matter in our bodies (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur) had existed on the planet at the time. An experiment performed by a scientist named Stanley Miller indicated that biomacromolecules could easily be produced when scientists reflect the conditions of the early planet, also supporting the abiogenesis hypothesis. Miller recreated the conditions of the early Earth in flasks; he filled a flask with water, methane, ammonia, and hydrogen, later sending electrical currents through the flask. Remarkably, the currents resulted in the genesis of five amino acids: the building blocks of proteins, themselves biomacromolecules. On a longer scale (perhaps hundreds of thousands or even million of years), these macromolecules could begin to form life. Though abiogenesis is the most accepted hypothesis regarding the formation of life on earth, there remains much we have to learn. There is neither evidence supporting nor refuting the theory, and we have never been able to model or even fully understand the process in the lab: we have never produced actual life when modeling this process, forwe cannot travel 3.9 billion years into the past and watch it occur for ourselves. We thus do not know entirely how the process actually works. There are still many things we must learn about our planet before we can determine the origin of life on it, but for now, we can continue to ponder one of the most heart-wrenching and controversial questions our species has ever considered.

The origin of our solar system and, especially, the origin of life is a difficult topic for any of us (including scientists) to understand. While we know so little that would be able to answer these questions, new discoveries are leading us closer to answering them.

If you have any questions, comments, or corrections, please comment on this post or email learningbywilliam@gmail.com with your concerns. Thank you.

References

Accretion and Solar System Bodies. (n.d.). Retrieved from https://www.teachastronomy.com/textbook/How-Planetary-Systems-Form/Accretion-and-Solar-System-Bodies/

Allgre, C. J. (2005, July 01). Evolution of Earth. Retrieved from https://www.scientificamerican.com/article/evolution-of-earth/

Canup, R. M. (2019, May 31). Giant Impact Hypothesis: An evolving legacy of Apollo. Retrieved from https://astronomy.com/news/2019/05/giant-impact-hypothesis-an-evolving-legacy-of-apollo

Four Major Characteristics of the Solar System. (n.d.). Retrieved from http://www.astro.umass.edu/~myun/teaching/a100_old/solarnebulartheory.html

Smithsonian National Museum of Natural History. (n.d.). Retrieved from https://forces.si.edu/atmosphere/02_02_01.html

Than, K. (2016, September 01). How Did Life Arise on Earth? Retrieved from https://www.livescience.com/1804-greatest-mysteries-life-arise-earth.html

Yong, E. (2019, October 07). Scientists finish a 53-year-old classic experiment on the origins of life. Retrieved from https://www.discovermagazine.com/planet-earth/scientists-finish-a-53-year-old-classic-experiment-on-the-origins-of-life

Abiogenesis. (n.d.). Retrieved from https://www.britannica.com/science/abiogenesis