Monday, December 30, 2013

Origin of Life on Earth – Part 1: Primordial soup or soups?



The origin of life is a fascinating tale of how chemistry turned into biology. To trace the beginnings, we have to figure out how raw material available on earth combined to form complex macro-molecules such as lipids, amino acids and nucleotides – the building blocks of life.

Chemical reactions do not take place in benign environments. All chemical reactions need energy - some need less and some more. Even reactions that appear to occur spontaneously, such as sodium instantly reacting with water, will do so only at a certain temperature and pressure. Lower one or both and nothing will happen.

A revolutionary chemical experiment was carried out by Harold Urey, a Nobel prize winning professor at the University of Chicago and his graduate student Stanley Miller in 1953. A mixture of simple gases that would have been present in Earth’s primitive atmosphere and gently boiling water to mimic the hot oceans were subjected to electric discharge that simulated energy through lightening. At the end of two weeks, analysis of the mixture revealed an abundance of amino acids and other bio-building blocks. Had Miller and Urey provided experimental support for the primordial soup theory posited by Soviet biologist Alexander Oparin in 1924? For several decades following the announcement of their results, a large section of the scientific community did indeed believe so.

The field of science is not exactly the place where one should hold on to a single point of view. That is fine if we know everything there is to know.

A team of “cave scientists” from the University of New Mexico, while trying to figure out how the intricate cave structures beneath the Guadalupe Mountains in the Carlsbad Caverns of New Mexico are formed, made some startling discoveries.

The generally accepted view on formation of limestone caves such as the Carlsbad Caverns is this: rain water absorbs carbon dioxide from the air and turns into carbonic acid and as it seeps through the rocks, over millions of years, this mild acid dissolves away the rock, thus shaping the cave. Within the cave, though they found an unexpected mineral – gypsum. Gypsum is easily dissolved in water and so if water and carbonic acid were indeed responsible to fashion these caves, there should not have been any gypsum at all. More curiously, what explains the presence of gypsum in the first place?

There is only one way this could have happened – with sulphuric acid. When sulphuric acid reacts with limestone, it dissolves carbonate, releases carbon dioxide gas and leaves behind gypsum. But where did the sulphuric acid come from? The team realized that hydrogen sulphide from the oil fields beneath the caves leaked into the caves and reacted with oxygen to form sulphuric acid. But what accounted for the hydrogen sulphide? What could be converting the oil into hydrogen sulphide deep underground?

Microbes! Microbes - living under extreme conditions of pressure and temperature, furiously at work, just by feeding off oil. With no sunlight, no water, no lightening – without most of the ingredients of the Miller – Urey experiment. Further evidence of this process has been found in Cueva de Via Luz – a cave is Southern Mexico.

The analysis of the Murchison meteorite and findings that it contains amino acids, sugars, lipids and nucleobases further strengthened the view that, life may have originated outside of our planet and delivered through the course of constant meteor bombardment of early earth. While conclusive evidence for this view is lacking, we can be certain that the meteors themselves have most of the ingredients needed for life.

Clearly there is no one magic formula to prepare the primordial soup. And no single place where this soup was made. All evidence points to many different soups being made in many different places using different recipes. 

What seems likely is that every ancient environment with sources of energy and basic ingredients could have produced its share of amino acids, sugars, lipids and other building blocks of life. 

The next  article will closely examine the hostile environment on early earth which provided the necessary cauldron where life’s raw material could be formed and the unique characteristic and roles of key players in this great process.

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