Origin of life

All livings things on Earth, both in the present and in the past, share a single, common ancestor that lived roughly 4 billion years ago.

Peter Russell, iGenetics

How biological life originated on Earth remains a profound mystery. Denton provides a basic introduction to the question when he writes:

…the first cell is supposed to have arisen following a long period of pre-cellular evolution. The process is presumed to have begun with a primitive self-replicating molecule which slowly accumulated beneficial mutations that enabled it to reproduce more efficiently. After eons of time, it gradually evolved into a more complex self-replicating object acquiring a cell membrane, metabolic functions and eventually all the complex bio-chemical machinery of the cell.

Michael Denton, Evolution: a Theory in Crisis

He then goes on to describe some of the issues that scientists face in providing a complete and credible explanation:

The existence of a prebiotic soup is crucial to the whole scheme [models for the origin of life]. Without an abiotic accumulation of the building blocks of the cell no life could ever evolve. If the traditional story is true, therefore, there must have existed for many millions of years a rich mixture of organic compounds in the ancient oceans and some of this material would very likely have been trapped in the sedimentary rocks lain down in the seas of those remote times.

Yet rocks of great antiquity have been examined over the past two decades and in none of them has any trace of abiotically produced organic compounds been found…Sediments from many other parts of the world dated variously between 3,900 million years old and 3,500 million years old show no sign of any abiotically formed organic compounds.

…In the presence of oxygen any organic compounds formed on the early Earth would be rapidly oxidized and degraded. For this reason many authorities have advocated an oxygen-free atmosphere for hundreds of millions of years following the formation of the Earth’s crust.

…Without oxygen there would be no ozone layer in the upper atmosphere which today protects the Earth’s surface from a lethal dose of ultraviolet radiation. In an oxygen-free scenario, the ultraviolet flux reaching the Earth’s surface might be more than sufficient to break down organic compounds as quickly as they were produced.

… “Catch-22…If we have oxygen we have no organic compounds, but if we don’t have oxygen we have none either.

Recently, an Australian group reported the remains of a simple type of algae in rocks at least 3,500 million years old, and other rocks almost as ancient in other parts of the world have also yielded evidence of life over the past few years.

…The most difficult aspect of the origin of life problem lies not in the origin of the soup but in the stages leading from the soup to the cell.

…The complexity of the simplest known type of cell is so great that it is impossible to accept that such an object could have been thrown together suddenly by some kind of freakish, vastly improbable, event. Such an occurrence would be indistinguishable from a miracle.

Michael Denton, Evolution: a Theory in Crisis

One of the possibilities that would bypass many of the obstacles Denton’s lists above is the possibility that the first life originated in deep oceans away from killing ultraviolent radiation and atmospheric oxygen, like the extremophiles today that thrive near hydrothermal vents deep in the ocean.

Even so, significant hurtles remain:

The problem of the origin of life is not unique—it only represents the most dramatic example of the universal principle that complex systems cannot be approached gradually through functional intermediates because of the necessity of perfect coadaptation of their components as a pre-condition of function.

…The only alternative is to consider the possibility of saltation. However, the probability of a sudden fortuitous event assembling the first cell de novo has generally struck most biologists as outrageously improbable. Yet, if gradualism is impossible, there may be no alternative but to presume that such an extraordinarily lucky accident was responsible for creating the first cell.

Michael Denton, Evolution: a Theory in Crisis

Another problem that faces scientists attempting to explain how life began is that...

...the simplest cells available to us for study have nothing “primitive” about them…no vestiges of truly primitive structures are discernible.

Michael Denton, Evolution: a Theory in Crisis

This means that we have no existing biological roadmap as to how the first cell might have developed. The world is filled with single-celled bacteria and many more complex forms up to and including humans, providing such a biological roadmap that at least includes major steps along the evolutionary way. But between naked chemistry and the simplest of cells (ones still remarkably complex), we have virtually nothing to go by, nothing that exists in nature (and rarely in a lab) that might provide crucial links that once evolved into the first living cell. “The only way to make a new cell is through division of a pre-existing cell.”

Richard Dawkins asks us to embrace the possibility of a tremendously unlikely combination of events in the distant past:

Suppose we want to suggest, for instance, that life began when both DNA and its protein-based replication machinery spontaneously chanced to come into existence. We can allow ourselves the luxury of such an extravagant theory, provided that the odds against this coincidence occurring on a planet do not exceed 100 billion billion to one.

But although we are entitled, in our theory of the origin of life, to spend a maximum ration of luck amounting, perhaps, to odds of 100 billion billion to one against, my hunch is that we aren’t going to need more than a small fraction of that ration. The origin of life on a planet can be a very improbable even indeed by our everyday standards, or indeed by the standards of the chemistry laboratory, and still be sufficiently probable to have occurred, not just once but many times, all over the universe.

Richard Dawkins, The Blind Watchmaker

In our exploration of a living cell we will review in detail the intricacies that Dawkins seriously suggests arose spontaneously, and put that notion to rest. Without some other (unknown) aspects of nature, the possibility that such molecular machinery could simply fall into place and function effectively is impossible. A proper explanation for the origin of life will include natural elements and not the probabilistic miracle that Dawkins suggests.

Another possibility exists, one we touched upon earlier. It’s possible biological elements simply exist as part of the fabric of the universe:

Information theorist Huber Yockey argues that the information needed to begin life could not have developed by chance; he suggests that life be considered a given, like matter or energy.

Michael Behe, Darwin’s Black Box

This seems highly unlikely, as the distance in complexity and substance between bacteria and basalt (that is, between the living and the non-living) represents the most profound gap in nature. That and the fact that we have yet to discern any evidence for life existing anywhere but Earth suggests that the existence of life does indeed merit special explanation.

A recent publication reviews the status of current Origin of Life (OoL) studies and what it will take to make significant progress in determining how life originated. The scientific community is challenged across several distinct disciplines to coordinate their research in order to succeed. The following model from the same article does a nice job expressing the state of OoL studies, the need for inter-disciplinary participation, and the principle questions that require attention:

Many theories have been expressed, as noted in the article:

The list of individual theories, different lines of experimental and theoretical research and diverse views on the OoL is extensive and eclectic.