How Did We Get Here? (Part 1)
Primordial Soup + Extraterrestrial Life
Rewind a couple of billion years, and you’ll find yourself in heaven on Earth. No more work, no more bills to pay, and no more awkward day-to-day interactions; you’re finally free of any burden or responsibility. Now, you can just sit back, relax, and listen to the soft bubbling of the magma. Welcome to the good life.
That is until you’re roasted alive.
Back then, there was a reason why no life had emerged yet. The air was an acrid smog of methane, ammonia, and water vapor; the ground was scorching hot; and the planet was covered with pools of magma.
So how did life form in this alien environment?
Idea #1: Spontaneous Life
“So with animals, some spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock”
— Aristotle, On the History of Animals
Aristotle may have been a brilliant philosopher and astronomer, but he fell short with his writings on evolution.
Over 2000 years ago, Aristotle believed that life generated spontaneously. To him, one of the methods of animal reproduction was just having offspring appear out of nothing.
Then came a man and his jars of meat. In the 1600s, Francesco Redi, a well-known Italian physician and scientist at the time, set out to disprove Aristotle’s theory of Spontaneous Generation. His experiment involved setting out multiple jars of meat with various amounts of covering: some completely covered with cork, some covered with a layer of gauze, and some left uncovered. Within a short amount of time, the uncovered jars were infested with maggots and flies, the gauze-covered jars had maggots on top of the gauze, and the covered jars had no maggots at all.
This proved that maggots appeared only because flies were previously there. For example, no maggots appeared near the cork-covered jars because flies never went near (impossible to get in and couldn’t smell the meat). Therefore, this meant that the maggots were offspring of the flies, which disproved Spontaneous Generation.¹
Idea #2: Primordial Soup
Ingredients:
- 10 billion gallons of water²
- Ammonia
- Carbon Dioxide
- Hydrogen
- Severe Thunderstorms
Procedure:
- Mix water, ammonia, carbon dioxide, and hydrogen until all the gases and liquids are evenly distributed (across the entire planet)
- Add severe thunderstorms for millions of years (provides phosphorous and energy)
- Let cool for a few more millions of years, and now take out your primordial soup with new organic compounds (that can be used to make life)!
In the 1900s, Aleksandr Oparin and J. B. S. Haldane believed life formed from a Primordial Soup, pre-life Earth’s gaseous and liquid makeup. They believed that all the liquids and gasses would interact and, with the help of lightning, form organic compounds.
In 1953, UChicago graduate student Stanley Miller and his supervisor Harold Urey set about proving the Oparin-Haldane theory. They set up a contraption with a mixture of the various pre-life gases and the addition of electrical sparks (to simulate thunder/lightning). And just after a week, they found numerous new amino acids, crucial components for proteins and life³, in their contraption.
However, the environment simulated by the Miller and Urey experiment is now believed to be an inaccurate representation of pre-life Earth. For example, the gasses used by Miller and Urey should have included more types, such as hydrogen sulfide, nitrogen, and sulfur dioxide. Regardless of its critiques, this experiment still provides a valuable framework of how life may have formed. As more and more scientific advancements are made, newer, more accurate renditions of this experiment will decide the validity of this idea.
Idea #3: Hydrothermal Vents
The silence is deafening down in the deep sea. Pitch-black darkness envelopes you, and a boiling heat scalds your body. Deep cracks line the ocean floor, exposing the magma underneath the Earth’s crust. You see water seep into the cracks before immediately being shot out as a jet of mineral-rich steam. These Hydrothermal Vents may have been the origin sites of life.
Due to the magma inside the hydrothermal vents, as water enters and shoots out of the fissures, new nutrients and minerals (from the magma) are also added to the ocean. This, along with the added heat from the steam, would create energy that can then be used to create and combine minerals and nutrients.⁴
This idea is further backed up by the LUCA (Last Universal Common Ancestor) of all organisms alive today. By taking all the shared genes between most organisms alive, scientists have come up with a rough picture of the life of LUCAs. LUCA lived in hot, anaerobic conditions and harvested energy from chemical gradients. Check, check, and check.
But, on second thought, hot and anaerobic conditions may be too broad. After all, that description could fit the pre-life land(no oxygen-producing plants yet), underground, and meteors.
Idea #4: PANSPERMIA
When you think of extraterrestrial life, you probably don’t think of this fourth idea. You might think of green aliens on UFOs or fleets of advanced spaceships, but, unfortunately, Panspermia is just an assortment of organic molecules on space rocks. This idea suggests that the first organic molecules were introduced to Earth through asteroids or meteors.
It’s not even an outrageous idea, though. Organic compounds, such as methane, methanol, and formaldehyde, have been created in environments mimicking that of outer space (near absolute zero temperature and harsh UV radiation)⁵.
Furthermore, instances of organic compounds on meteorites have occurred before. For example, the Murchison Meteorite, full of various amino acids, fell to Earth in 1969. If a similar meteorite survived the fall down to Earth, it could have been the origin of life.
But we may have got it all wrong. Maybe it’s not organic compounds that appeared first, but the tools used to make them.
Idea #5: RNA World
DNA’s single-stranded cousin, RNA, tends to be overshadowed by the more-known double-helix of DNA. Yet, RNA may have come before DNA, and it might just be the origin of life.
RNA may be one of the greatest tools for life because of its ability to both store genetic information and construct proteins using it. One type of RNA acts as a messenger that transports copied genetic information in cells. At the same time, three kinds of RNA work in unison to use that genetic information to create proteins.
Unlike the other ideas, “RNA World” suggests that RNA was the origin of life, not organic compounds (like amino acids). Furthermore, “RNA World” states that a self-replicating RNA molecule appeared on Earth at one point, either at hydrothermal vents, in primordial soup, or through Panspermia. The RNA started evolving from there, with the best RNAs (and their protein products) surviving. Eventually, a mutation may have turned some RNA into the familiar DNA double helix.
Although these ideas all have their merits, there is still no definitive answer on the origin of life. As research continues in this field, we will hopefully see new advancements and get a final answer. But no matter where we originated from, whether from Primordial Soup, Hydrothermal Vents, Meteors, or RNA, we should all appreciate how far life has come.
¹Back in Aristotle’s time, some people believed maggots were generated from rotten meat.
²These metrics are not accurate, but very rough guesses
³Amino Acids are indicators of life because they create proteins, one of the building blocks of life. Although they are not alive, they are a huge step towards life.
⁴This is a massive oversimplification of the hydrothermal vents. In reality, the hydrothermal vents create a huge temperature gradient (hot water from the steam vs. cold water surrounding) and a chemical gradient (because it spews out new nutrients). These gradients would have then been used for energy.
⁵https://www.biology-pages.info/A/AbioticSynthesis.html#Molecules_from_outer_space?
