Imagine the origin of life on Earth four billion years ago as a kind of ‘black box’ floating in the air. Below the box, earliest Earth is all chemistry: rocks, gasses, liquids, and other physical (inorganic) elements. Above the box, biology has appeared in the form of rudimentary cellular (organic) life. The box blocks our view of what links the two, hiding an extraordinary mystery: how did life happen when no life existed previously? How does chemistry, in other words, produce biology? Scientists don’t know the answer yet, but they are getting closer. In Charles Darwin’s day, the black box was huge; today it has shrunk dramatically, thanks to countless experiments and hundreds of researchers. While its contents are still a mystery, two theories have emerged about what happened inside the box all those years ago.

Let’s take a step back first.

The basic unit of all life is the cell, the smallest unit on the planet classified as a living thing. Cells have the same essential parts: interior and exterior membranes that regulate molecular traffic into and out of the cell; proteins that catalyze chemical reactions; a ‘library’ of information in the form of DNA which the proteins continually consult; and RNA, errand-runners who provide blueprints for the formation of new proteins. A cell is a complete package – it has everything it needs to grow and reproduce, provided it has access to minerals and energy in its immediate environment. The chemical process that enables a cell to transform these elements and energy into action is called metabolism. Its presence, along with replication and evolutionary change, is the foundation of life on Earth.

A cell is a sophisticated organism, but in the early, harsh days of Earth’s history, life had to be much simpler – but not too simple. It’s the Goldilocks Principle: organic life had to be simple enough to be created by inorganic processes and yet complex enough to replicate itself and initiate evolution. Life had to be just right – ‘hot’ enough to be weaned from the physical processes that gave it birth, but ‘cold’ enough to synthesize molecules and tap chemical nutrients and solar energy in order to fuel its cells. The just right part was the creation of metabolism, scientists say. But how did metabolism come to be?

One theory targets RNA as the likely suspect. Experiments have demonstrated that in the presence of certain mineral catalysts, nucleotides, which are molecules that form the building blocks of life, can join together to form RNA (though nucleotides themselves have not yet been built from scratch in a laboratory). Furthermore, it is has been observed that relatively short RNA molecules can author their own replication, which is the first big step toward metabolism. However, a second theory says proteins can do the same thing – as the famous Miller-Urey experiment demonstrated back in the 1950s when it proved that amino acids can form under inorganic conditions. This is another path to metabolism. Thus, depending on environmental conditions, RNA and/or proto-proteins could have evolved in primeval oceans.

Not surprisingly, there’s a third theory: metabolism came first, followed by RNA and proteins. This theory, which was considered quite radical when it was first proposed a few years ago, involves thermal vents, deep undersea, where hydrogen sulfide from a vent reacts with iron monosulfide, lying around, to create pyrite, a common mineral commonly called ‘fool’s gold.’ It is a process that allows the fixation of carbon dioxide, found in the seawater, forming organic compounds on the pyrite, leading to the creation of the basic functions of metabolism. The nucleic acids and proteins came later.

And of course, carbon is involved in nearly every stage of these processes.

The riddle of life’s origin is a classic chicken-and-egg question: were RNA and proteins required to create metabolism, or was it the other way around? Which came first? Complicating matters further is the question of where DNA originated. Molecular ‘cross talk’ between nucleic acids and proteins, necessary for a cell’s growth and replication – and with it the emergence of complex life – is mediated by its genetic code. But where did DNA come from? There is no evidence (yet) that it can be created by the same inorganic process that jump-started metabolism. Dr. Francis Crick, one of the two scientists who discovered DNA, believed its creation had to be a cosmic “accident” – possibly the result of a DNA-carrying meteor or comet hitting the planet during its formative years. The only thing scientists can say for certain is that the origin of DNA is a holy grail still locked deep inside the black box.

Here’s a picture of a thermal vent on the ocean floor:

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Is a computer alive?

After all, a computer is a type of cell. It has a membrane through which energy and bits of data flow; it has DNA-like coded instructions in the form of programs and files that are constantly being changed and updated; its codes and files can be copied and shared with other computers; it has RNA-like wiring that carry electrical messages; it has a kind of metabolism, consuming electricity from its environment, generating paper printouts and creating heat as a waste product. And there’s lots of carbon in a computer – silicon too. It’s a carbon-and-silicon-based life form!

Of course, a computer is not alive. For one thing, it can’t reproduce itself, not yet anyway. Cells make copies of themselves, which is how an organism grows, and computers cannot do this, or else Apple and Dell would be out of business. Robots might be a different matter, however. Science fiction is littered with dark fantasies about self-reproducing robots run amok, usually the violent expense of humanity. Is it a possibility? Here’s a list of what biologists consider the basic ingredients of life: living things take in energy; they get rid of waste; they grow and develop; they respond to their environment; they reproduce and pass their traits onto their offspring; they evolve in response to their environment. Sounds like a robot to me! Yikes! But are robots alive? This question might be moot if one were coming at you with a laser gun in its metallic (inorganic) hand.

What is life?

It’s not a philosophical question. Recently, scientists have developed the ability to transfer DNA from one cell to another, changing its genetic makeup and creating an organism didn’t exist before. This new cell functions exactly like every other cell found in nature according to the definitions of life. And this is just the tip of a very large iceberg too. Teams around the planet (often working for profit-making private firms) are trying to create life in a variety of forms, including from inorganic sources. They’re trying, in other words, to shrink down the black box to zero. The best guess is they’ll accomplish this goal in less than ten years.

At the same time, scientists are hard at work trying to redefine death. What does it mean to die? Is it simply the opposite of life? Can it be delayed, interrupted, or stopped? Is this even a good idea?

Beats me. Intuitively, I suspect these developments are not good things, or at least not in the long run. We’re likely to provoke the Law of Unintended Consequences by playing God, reminding me of a classic satirical Onion headline: “New Technological Breakthrough to Fix the Crisis Caused by the Previous Technological Breakthrough.” I suppose at the rate we’re going, we’ll know soon enough.

In the meantime, I’ll settle for lyrics written by former Beatle George Harrison in his 1970 hit What is Life?

What I feel, I can’t say
But my love is there for you anytime of day
But if it’s not love that you need
Then I’ll try my best to make everything succeed

Tell me, what is my life without your love
Tell me, who am I without you, by my side

What I know, I can do
If I give my love now to everyone like you
But if it’s not love that you need
Then I’ll try my best to make everything succeed

Tell me, what is my life without your love
Tell me, who am I without you, by my side
Tell me, what is my life without your love
Tell me, who am I without you, by my side

Listen for yourself: http://www.youtube.com/watch?v=8eEQ4J6Lnrs

george-harrison-what-is-life-apple-7

 

 

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