Supporting Evidence 1

What is life?

There is no simple definition of life. According to the Reader's Digest Great Illustrated Dictionary, p.979, life is defined as:

"The property or quality manifested in functions such as metabolism, growth, response to stimulation, and reproduction, by which living organisms are distinguished from dead organisms or from inanimate matter."

Technically, this definition could be applied to a piece of crystal, as it can grow over time as if it were alive, break apart as if were reproducing, and continue to grow. Does this mean that all matter can be considered alive?

The Russian biochemist, Dr Alexandr Ivanovich Oparin (1894-1980), a former professor at Moscow University, kept the definition of life simple and elegant when he said back in 1924:

"There is no fundamental difference between a living organism and lifeless matter. The complex combination of manifestations and properties so characteristic of life must have arisen in the process of the evolution of matter." (1)

By Oparin's standards this would mean that life is indeed unimaginably common and our question of "Are we alone?" would already have been answered. However, scientists don't like to make this the shortest discussion in history. Instead, scientists like to drag it out a little more by providing more details of what they think is the accepted point at which life begins.

Deoxyribonucleic Acid (DNA)

Inside the nucleus of every living cell is a special molecule considered crucial to the development and evolution of life on Earth. On Earth, the scientists call it Deoxyribonucleic Acid (DNA). Most commonly found in its coiled and wrapped up state, these rigid and compact rod-like structure known as a chromosome, DNA in the unwrapped state is an extremely long and thin thread-like molecule designed to hold a great deal of biochemical and genetic information over the long-term, as needed to replicate itself (genetically) and to cope with its environment (biochemically). As Murray Gell-Mann of the California Institute of Technology said:

"In biological evolution, experience of the past is compressed in the genetic message encoded in DNA." (2)

How is information encoded in DNA?

Genetic and biochemical information is encoded along active segments of the DNA as a long sequence of nucleic acid bases attached to a very strong backbone of phosphates and deoxyribose sugar support structures. The nucleic acid bases are broadly composed of two types: purine and pyridimine bases. The names given to the purine bases are adenine and guanine, while the pyridimine bases are cytosine and thymine. For simplicity sake, scientists tend to use the letters A, C, T and G to represent these nucleic acid bases. The entire phosphate-sugar-base subunit is termed a nucleotide. Thus there are only four fundamental nucleotides that make up the code of life here on Earth:

Adenine (A)
Cytosine (C)
Thymine (T)
Guanine (G)

And any active segment of the DNA that carries instructions for building a protein is called a gene.

Thus the complete set of genes running along the various active sections of the DNA (or active sequences of nucleotides, wherever they may be) determines not only the species of animal or plant that will develop into a living thing, but also the individuality of the living thing within a species. This means that any change made to any active sequence of purine and pyridimine bases (or nucleotides), for whatever reason, constitutes a mutation, which may alter, gain or completely lose, the original function", shape and/or behaviour of the living organism.

How do cells know what to do?

Every living cell in an organism contains an exact DNA replica or "blueprint" of the code of life. What makes one group of cells perform differently from another group within the body of a living organism is the range of different proteins produced from specific active sections along the DNA that tell the cell how to do things. However to avoid cells from getting mixed up in their functions, DNA is able to switch off specific genes and allow other genes to create the relevant proteins needed to control the cell.

Keep in the mind that proteins are chains of amino acids of which only 22 different types of amino acids are used by life on Earth, as shown in the following table (3):

Amino Acid	Symbol	Chemical Formula
Alanine	Ala	C3H7NO2
Arginine	Arg	C6H14N4O2
Asparagine	Asn	C4H8N2O3
Aspartic Acid	Asp	C4H7NO4
Cysteine	Cys	C3H7NO2S
Glutamic Acid	Glu	C5H9NO4
Glutamine	Gln	C5H10N2O3
Glycine	Gly	C2H5O2
Histidine	His	C6H9N3O2
Hydroxyproline	Hyp	C5H9NO3
Isoleucine	Ile	C6H13NO2
Leucine	Leu	C6H13NO2
Lysine	Lys	C6H14N2O2
Methionine	Met	C5H11NO2S
Phenylalanine	Phe	C9H11NO2
Proline	Pro	C5H9NO2
Pyroglutamatic Acid	Glp	C5H7NO3
Serine	Ser	C3H7NO3
Threonine	Thr	C4H9NO3
Tryptophan	Trp	C11H12N2O2
Tyrosine	Tyr	C9H11NO3
Valine	Val	C5H11NO2

Knowing how important these active coding sequences are for the healthy functioning of the cells and the living organism, DNA has found a way to maximize the preservation of this information through the use of dummy or nonsense coding sequences. Also known as introns or just plain "junk DNA", these non-active coding segments are thought to play a role in providing adequate separation between active sequences (called exons) and further protecting the relevant active codes when DNA is properly wrapped up into its more rigid rod-like structure.

What does DNA look like?

DNA is a double helix, which means it looks like a twisted or spiral ladder. The sides of the ladder are the phosphates and sugars, while the rungs of the ladder are where the nucleic acid bases are located. The then 25-year-old American biologist James D. Watson working with Francis H. Crick, an English physicist at the University of Cambridge are credited with establishing the structure of DNA in 1953 using the process of X-ray crystallography. Further details of this work can be found in the original article (4) published by Watson and Crick titled "Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" in the British journal Nature.

How is DNA information read?

For the information to be read, the DNA has to undergo a delicate process of unzipping a portion of the code. A smaller and more agile version of itself, called messenger Ribonucleic Acid (mRNA), then passes through the membrane of the cell nucleus and reads the coding sequence on the DNA, where it is transcribed into its own nucleic acid bases. Once it has the information, it runs back to tell the "ribosomes" how to assemble the amino acids into a protein.

Structurally, there isn't a great deal of difference between DNA and mRNA, except that mRNA is a smaller single strand of the DNA. However, mRNA does not use thymine. Instead another nucleic acid base called uracil (U) replaces the thymine.

When an active coding sequence is read, mRNA is able to grab up to 3 nucleotides of information at a time and will continue to read further sets of 3 nucleotides until the entire sequence of amino acids for the protein has been determined. For example, a potentially complete active sequence of three nucleotides on DNA represented by the letters ATG and read by mRNA as AUG (remember, uracil is used instead of thymine) is sent to the ribosome where it assembles the amino acid known as methionine. If mRNA grabs the complete coding sequence from DNA consisting of nucleotides that form the letters TGT TGC (or UGU UGC from the perspective of mRNA), this is enough information for the ribosome to produce the amino acid called cysteine.

TTT	Phe	TCT	Ser	TAT	Tyr	TGT	Cys
TTC		TCC		TAC		TGC
TTA	Leu	TCA		TAA	Stop	TGA	Stop
TTG		TCG		TAG		TGG	Trp
CTT	Leu	CCT	Pro	CAT	His	CGT	Arg
CTC		CCC		CAC		CGC
CTA		CCA		CAA	Gln	CGA
CTG		CCG		CAG		CGG
ATT	Ile	ACT	Thr	AAT	Asn	AGT	Ser
ATC		ACC		AAC		AGC
ATA		ACA		AAA	Lys	AGA	Arg
ATG	Met	ACG		AAG		AGG
GTT	Val	GCT	Ala	GAT	Asp	GGT	Gly
GTC		GCC		GAC		GGC
GTA		GCA		GAA	Glu	GGA
GTG		GCG		GAG		GGG

But because many functions of a cell require proteins, numerous amino acids usually have to be assembled into a chain. This means that the active coding sequence of DNA to produce a protein can be potentially be very long.

Fortunately, not all physical characteristics of a living organism require complex proteins to control them. There are some characteristics that can be controlled by just a handful of selected amino acids arranged in a particular combination to help make the right protein. The table below gives an example of how human hair colour can be changed by a handful of amino acids:

AMINO ACID CHAIN	COLOUR
Met - Ser - Thr - Gln - Phe	Red hair
Met - Ser - Thr - His - Leu	Blonde hair
Met - Pro - Thr - His - Phe	Black hair
Met - Pro - Thur - Gln - Leu	Brown hair

Why must DNA replicate itself?

To understand why DNA replicates itself, it is necessary to explain how the environment plays a crucial role in this process.

Imagine that we live in a universe that contains no radiation. Impossible in reality, but just imagine such an environment. Assuming that matter could exist in this environment, we would discover an interesting fact: nothing would move. In other words, there would be no collisions. In the absence of collisions, atoms of different elements would not be formed. Complex molecules would never be produced. And virtually life would not exist. And that includes the genetic code and DNA itself. But if, in the slightest possibility, it could, a universe free of radiation, DNA would not need to spiral and wrap itself up into a tight rod-like structure called a chromosome. It does not need this rigidity in the DNA because there is nothing in the environment to collide with DNA to cause it to break apart. However, as soon as you turn on the switch and let radiation flood the universe, DNA has not only got to swim in this radiation-filled environment, it must also protect itself as best it can from the ravages of some high-frequency radiation coming in and potentially having enough energy to break DNA apart.

It means DNA has to be protected as best it can. The better it is protected, the longer the genetic information is retained and able to provide the information needed for the body to perform its tasks.

Rocky planets are truly a godsend for atoms and molecules that need to attain stability and preserve their chemical structures. The great piece of rock in space composed, mostly made up of iron, provides an excellent shield over one side of the DNA (which is why the DNA produced for reproductive purposes tend to be lower down and between our legs as the rest of the body and atmosphere provides the final level of protection from the radiation, while the ground and planet provides the greatest protection on the opposite side) and greatly reduces the number of collisions with molecules and atoms. Not only that, but the atmospheres of these planets provide further protection for atoms and molecules.

Even so, radiation from space and other matter will concentrate around a rocky planet and continue to fall into it like a sinkhole. Fortunately much of this radiation has reduced frequency or energy after colliding with the atoms in the atmosphere, the human body, and the ground and planet's rocky and molten iron core to bring it into the safer range. The kind of range more suited to the development of life on Earth.

But if, for any reason, the radiation (and other foreign forms of matter) is sufficiently energetic, electrons mcanay be stripped from atoms, and chemical bonds between atoms to form molecules can break apart. The resultant partial molecular fragment is often charged (either by a loss of one or more electrons to be positively charged, or the addition of one or more electrons to be negatively charged) is known as a free radical. Fortunately, there are regular brief moments when the energy dissipates, allowing these free radicals to quickly reassemble into larger and more complex organic molecules designed to neutralise the excess charge. Or else enough waterr molecules can surround or react and neutralise the charge. That's why drinking plenty of water helps astronauts to neutralise the excess charges built-up in the body while working in space.

Should this molecular break-up occur in DNA, it can be potentially bad news. Or, in rare cases, it could be potentially good news. This depends on the type of mutations formed in the genetic code of the DNA after the molecule is repaired. If the repair is perfect, there will be no mutations, but if not, it could help to produce a better organism. An organism that is more resilient, tougher, stronger and/or have characteristics that make it unique and more adaptable to the local environment in which it lives.

The only way to reduce the number of molecules getting broken apart from collisions with radiation or other foreign matter is simply to find places to protect them. For example, if these molecules can get into tiny raindrops, or fall closer to the surface of the planet, they will be better protected. A more substantial supply of water by way of shallow seas do help to increase the protection for developing and highly complex organic molecules. It means that larger molecules can survive for longer with fewer collisions when surrounded by copious amounts of water molecules. Also, hang around near the surfaces of clays can see the molecules inadvertently receive greater protection. Then the molecules can grow on these surfaces into larger structures under the right conditions and in the presence of certain metals, such as zinc. Once the molecules are long enough, the extra chain length can help to wrap itself into a tight-fitting structure for further protection. Some other chains also develop a spiralling structure with its backbone of atoms acting as a barrier against radiation and other matter as it protects something important in the centre of the molecule to help further achieve its goal of greater stability (sounds familiar?).

Well, this is what DNA does to protect its genetic code.

Need more protection? No problem. In fact, water provides further protection by forming tiny bubbles. The molecules held inside can survive longer than they would without the bubbles. Add another layer of protection by way of a spherical membrane made of protein to hold the water inside, together with the important molecules you are trying to protect, and it is possible to carry this bit of watery protection from the radiation around with you to different locations, even in the event where water in the environment has dried up. Here we have the first single cell organism.

Another membrane within a membrane provides yet another extra layer of protection in what we know of as the nucleus of the cell where the DNA resides.

In fact, DNA is often found inside the nucleus of a spherical cell as if trying to protect itself from something in the environment. This tells us that DNA is designed to preserve its information by developing proteins to act as a barrier against radiation and other foreign objects, and to give the organism the required functions and features of a brain, arms and legs, eyes, ears and so on as needed to defend itself and repel objects in the environment that can collide and potentially interfere with this aim of DNA to survive, replicate and transfer its genes. Anything to make it easier for the organism to protect itself for long enough in order for the DNA to do its job for as long as possible. As a further mechanism for preserving genetic information, it will make multiple copies of itself and store these new DNA within its own living cells. So, having multiple copies of itself everywhere, basically as many as you can make, increases the probability of preserving the genetic code.

DNA is a selfish gene. In order to survive, it must reproduce itself, and quite incessantly because of one factor: radiation.

This brings us to the fundamental reason why DNA has to replicate itself and does so all the time. It has to do with the intrinsic nature of the universe, which we call change, instigated by the forces of radiation (and other matter) that causes interference to the purpose of DNA. You see, self-replication is a natural and direct response to constant changes in the environment by rebuilding, repairing and ultimately preserving the genetic information it has acquired over billions of years on Earth as a way of balancing this change by creating stability in its genetic code.

What are mutations?

Despite the power of self-replication, or even setting up the barriers by DNA or the organism to protect itself, nothing is ever perfect in a universe filled with radiation and while the organism's understanding of this fact remains limited. At some point the organism must be exposed to such changes in the environment in order to gain enough experiences so as to help it understand the knowledge of how to survive better in the environment. DNA may have discovered an almost perfect system for handling changes in the environment. However, the relentless collisions and interference by other matter including radiation itself will eventually affect this self-replication process for DNA. It is during these rather precarious moments when DNA is in the process of self-replication or when it must provide the biochemical information of how to build proteins where it can be forced to record slight changes in the genetic code known as mutations..

Not all mutations are bad. Some mutations can improve an organism's ability to better handle its environment and, therefore, survive for longer. But other mutations may not be beneficial. It is here in these latter mutations that natural selection tends to eliminate the propagation of the wrong or non-beneficial mutations.

When does life begin?

We have gone into considerable detail in explaining DNA. You may be wonder why the emphasis? It is because DNA is the moment when scientists are certain that life will definitely appear. In other words, the sequence of purine and pyrimidine bases that make up that all-important self-replicating macromolecule called DNA is where scientists believe all the essential amino acids, enzymes and other vital chemicals needed to build the very stuff of life come together to create a living organism here on Earth. But it isn't just on Earth. Scientists think the same must be true of life throughout the universe. If life on another planet is to learn from its environment and find ways to protect itself and preserve the information for future generations, ETs must use a DNA-like molecule in their alien cells. ETs may not use the exact coding sequence or even the use of specific purine and pyrimidine bases in their biological cells. However, scientists are confident that a DNA-like molecule must exist.

So, if we do see alien life in the universe, a DNA-like molecule is expected to be found. And, indeed, the presence of this molecule is perhaps the only guaranteed proof scientists have that we have witnessed alien life. For there is nothing anyone can do to fake seeing an alien organism. It is impossible to do if the DNA-like molecule exists, shows differences in its structure, and the inevitable application of that DNA has led to the formation of alien life.