The Earliest Emergence of Life

The Earliest Emergence of Life

So many things have changed on this planet in the past 3.5 billion years or so that it is very difficult to re-create in a laboratory exactly the same conditions as existed back then--just the right "mix" of temperature and energy and just the right proportions of chemical compounds (such as methane, ammonia, carbon monoxide, water vapor, etc.) that existed in earth's early atmosphere. But even though no one has yet been able to fully recreate the emergence of simple life forms in a test-tube, scientists are getting closer all the time to being able to do just that. Beginning with Stanley Miller's famous experiments in the 1950s, a number of lab experiments have demonstrated that some of the basic chemical building blocks of life (including sugars and the basic components of proteins and DNA) will actually begin to coalesce ("self-assemble") spontaneously (on their own) given the right physical and chemical environment!

To qualify as a "life form"--rather than as an inanimate (non-living) object--a bit of matter has to have two main characteristics:

1) the ability to actively extract energy from the outside environment (such as when living plants derive energy from the sun, or when living animals derive energy from eating) and,

2) the ability to replicate itself: to qualify as "alive," matter has to be able to make copies of itself (though not necessarily perfectly identical copies) and in replicating itself it has to be able to "pass on" at least some of its characteristics to its descendants.

On this planet at least, all life forms also form some kind of membrane or compartment-- such as a cell membrane--which serves to contain the replication and energy-tapping mechanisms and keep them relatively separate and distinct from the rest of the outside world. Most scientists today think that the earliest living organisms on earth were little more than self-replicating protein molecules enclosed in a simple membrane,and that all subsequent life forms evolved over millions and billions of years from these simple beginnings.

Scientists began to experiment with recreating the initial steps in the emergence of life in the 1950s, and much progress has been made just in the last few decades. Even back in the 1950s Stanley Miller's laboratory experiments showed that simple chemical reactions could in fact produce some of the simplest building blocks of life: for instance, combining jolts of electrical energy (as could be supplied to an early environment by lightning) with a mixture of methane, ammonia and water (all of which also existed in the early atmosphere of our planet) has produced, among other things, some amino acids and sugars which are fundamental building blocks of more complex molecules in all living organisms . So, in the likely chemical and electrical conditions of the early earth (and, importantly, in the absence of anything around which could eat any of these building blocks of complex organic molecules!) the early oceans could well have become rich and concentrated "soups" of these substances, which may well have spontaneously come together to form simple interactive organic films or mats clinging to the ancient rocks or drifting in the ancient seas.

Some more recent laboratory experiments have even demonstrated that certain simple sequences of amino acids (short bits of RNA for instance) will sometimes self-replicate , or make copies of themselves, even in the absence of any protein enzymes (which until recently were thought to be absolutely required for this process to occur), and these new bits of RNA have even been observed beginning to evolve on their own! Given the right mix (or chemical "soup"), fatty acids- -which are key components of living cell membranes--have also been shown to assemble spontaneously--suggesting that some kind of similar process may well have been involved in the formation of the very first living cells . Again, the first living cells are likely to have been little more than tidbits of self-replicating DNA or RNA molecules surrounded by a simple membrane. Experiments investigating and demonstrating how the earliest forms of life might have emerged on this planet have been going on for only a few decades, so there is obviously still much to discover about these processes. But what has already been learned through these experiments clearly demonstrates how some of the first steps involved in the development of primitive life could have taken place spontaneously (without the hand of any divine "Creator" or "Intelligent Designer") in the primeval chemical "soup" of this planet.

Beyond that it is very important to understand that, while every detail of the process of the earliest emergence of life hasn't yet been fully worked out, scientists do know that life evolved after it emerged. And as we will see, there is actually a great deal of concrete evidence and proof of how this process has actually taken place over the past 3.5 billion years. [Return to "The Science of Evolution, Part 1"]