Creating the Primordial Soup in the Lab
The Miller — Urey experiment created the amino acids, the building block of life, in condition similar to that of early Earth. What happens after the formation of amino acids?
Where did life come from? That’s a question everyone wants an answer to.
If you are into ‘God’ then the answer is simple. GOD MADE EVERYTHING UP FROM NOTHING! How? Well, that varies from religion to religion.
But if you are not into that then we go to the next best thing. Science. So, you ask science how did life begin?
This is one of the many questions science does not have an exact answer but has many hypotheses. This is the story of that one hypothesis.
All the living cells are made of a few key long complex polymers which are made from simpler units such as amino acid and sugar.
Darwin introduced the concept of ‘warm pond’ model as a site for the origin of life.
So, in the 1950’s Stanely Miller and Harold. C. Urey inspired by the DIY culture decided to check whether organic molecules can be formed from inorganic compounds on its own without the divine intervention.
Spoiler Alert: Yes! They can.
The Experimental Setup
They took two flasks, one containing water and the other containing gases (methane, ammonia and hydrogen) resembling early Earth’s atmosphere.
(PC - Encyclopedia Britannica)
The water within the flask is heated to facilitate the movement of water and gases through the system. Meanwhile, water, along with water-soluble reaction byproducts, is condensed from the flask labeled as the "atmosphere" and subsequently precipitates into the "ocean."
This experiment requires an extraordinary degree of cleanliness to avoid false positive results.
A spark discharge, emulating lightning, energizes the chemical reaction.
The experiment lasted a week, and the setup changed color. A red and yellow solution collected in the trap, turning into a reddish-brown mixture by the end.
This was the amino acids they intended to make.
(PC - From Dust to Life)
Eureka! Eureka!
Hold on a minute. I said in the beginning that science do not have the answer to the ultimate question of the ‘life, the universe and everything’ (Although Douglas Adams had the answer, and it was ’42’ but that’s a story for another day).
Amino acid is the building block of life, and they combine together to form protein. But the thing is protein synthesis on its own is astronomically low probability event.
Our body does this, but protein synthesis is a complex process that requires a lot of stuff to happen. You need DNA, RNA, ribosomes, amino acids, tRNA, protein factors, and energy and we had nothing at that time.
Our body is a pretty complex machine. The Earth did not have anything except for amino acids and extreme conditions.
What we have here are ingredients of a cake. But just having the ingredient of the cake does not produce the cake.
Earth at that Time
The era we are talking here is Hadean age which was 4–4.5 billion years ago. The Earth was young and hot ball of mess.
O₂ was absent and CO₂ was 100–1000 times greater than today. The oceans were likely acidic with pH between 5 and 7.
(LibreTexts Geoscience)
The surface temperature was in the range of 230 °C and pressure was 27 above atmospheric pressure.
The conditions were not suitable for life, at least for our kind of life. But it got better for us to exist.
What happened after amino acid?
We actually don’t know what happened after formation of amino acid, but scientists can speculate and speculate they did. Amino acids could have
- reacted with each other to form peptide bonds,
- reacted with each other to form polymers,
- reacted with other molecules, such as nucleotides, to form more complex molecules.
We have entered the realm of could have and would have. Since this is just a hypothesis that’s all they can say.
But forming complex molecules is not an easy task.
Polymerization of amino acids into peptides, or nucleotides into RNA, is thermodynamically unfavorable in liquid water.
Problems With the Experiment
Some naysayers says that the actual conditions on the early Earth were way more complex than the experimental set-up.
Even if amino acids were formed, the way from amino acid to complex polymers or proteins is highly improbable one.
The doubts gave rise to many hypotheses such as ‘RNA World’ in which life begin with RNA molecule or ‘Panspermia’ which suggests that simples life forms may have come from meteorites or comets. You know the classic ‘aliens did it.’
I personally believe in the ‘RNA World’ hypothesis.
Sources
- The Possibility of Life — Jaime Green
- From Dust To Life — John Chambers and Jacqueline Mitton
- The Vital Question — Nick Lane
- https://www.britannica.com/science/Miller-Urey-experiment
