Revealing the Origins of Life – PBS (2011)

How life began is a very fundamental question. This short documentary is an outstanding primer for scientific explanation of the origin of life. Featuring Nobel prize winner Jack Szostack of Harvard University and John Sutherland of University of Manchester, it explains the chemical evolution leading to the formation of RNA. Scientists all agree that formation of basic building blocks of life is suprisingly very easy. The burning question is how do they react to form complex molecules?

RNA world hypothesis has been gaining momentum in discussions about what might have been the first hereditary information storage in prebiotic life. The hypothesis predicts that RNA was the precursor molecule organizing the flow of genetic information in first life forms emerged 3.9 billion years ago soon after the crust of the earth solidified. In modern living cells we call this genetic information flow as the Central Dogma.

RNA world hypothesis deals with prebiotic, pre-cellular stages. RNA is so capable of doing many tasks that it helps scientists bypass the classic “chicken and egg” style circular arguments. RNA can store genetic information just like DNA and can carry out chemical reactions like enzymes. So how RNA formed in the first place had been a hot topic. In this regard, Sutherland’s research is arguably among some of the most important ones since 1952 Miller-Urey experiment. Miller demonstrated that conditions in prebiotic earth were right for the formation of life. He showed how raw ingredients formed following ordinary rules of chemistry but didn’t show how life might have started.

RNA comes in a variety of different lengths. If we consider DNA as a book then RNA can be likened to a paragraph or a sentence (messengerRNA). It can even be as short as a single word (microRNA). Letters forming DNA (A,C,G,T) and RNA (A,C,G,U) are called nucleotides. Sutherland’s research has provided a recipe for the formation of two nucleotides that make RNA chain. Researcher’s used the “warm little pond” conditions that has been coined by Charles Darwin in a letter he wrote to botanist Joseph Hooker in 1871:

“It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present.— But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter would be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.”

“Warm little pond” idea is a good first approach to imagining a gentle environment where life has begun. First cells lacked the pump and valve machinery that maintains higher gradients of essential ions such as potassium, zinc, manganese and phosphate inside of them. Therefore these elements must be in high concentrations in environments where protocells began to take shape. Geochemical compositions of marine environments around 3.9 billion years ago couldn’t be able to maintain such high concentrations. Accordingly, the first cells must have evolved in shallow ponds of condensed, cool geothermal vapor probably lined with porous silicate minerals mixed with essential ions. Darwin’s reasoning therefore was quite plausible.

However scientists are coming up with more possibilities. Hydrothermal vents and sub-ice brinicles are some of the habitats thought to cradle early life by serving as hatcheries for first cells that can copy themselves.

Hydrothermal vents found along deep ocean ridges where continents separate from each other have always been a very strong candidate for origins of life. These hot water vents are loaded with dissolved minerals and form sponge-like vertical tubular structures called chemical gardens.

Conversely, there is another hypothesis that favors cold origins. Our sun was 30 percent less bright 4 billion years ago. As a consequence our planet was exposed to a few very dramatic “snowball earth” periods where entire liquid on the surface was frozen from pole to pole. Water is a unique molecule. Contrary to most other minerals when it freezes it becomes less dense and floats. Calculations of Jeffrey Bada of Scripps Institute of Oceanography has shown that the frozen fraction of oceans would be about 300m deep and there must have been very cold but unfrozen seas beneath this layer. Indeed this kind of physical environments still exist today. Brinicles are another form of chemical gardens. One of them was filmed for the first time during its formation by two cameramen Hugh Miller and Doug Anderson who set up a timelapse rig for the BBC series Frozen Planet.

Revealing the Origins of Life is a part of the full-feature PBS documentary titled “Where Do We Come From?” that was aired in 2011.

If you want to know about important events that happened after life has emerged all the way until the famous Cambrian explosion, you might want to check out the first part of a BBC documentary series called “First Life”.

 

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