Life in the Beginning
If you think that there is no other Life out there - then think again!
Life in the Beginning |
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What is Life |
Building blocks of life are in space
In the 1960s the hydroxyl radical (OH) was identified by astronomers in these interstellar clouds, as was ammonia (NH3). Later water (H20) was identified soon to be followed by the important organic molecule formaldehyde (H2CO).
At the beginning of this century there have been over 100 organic molecules identifed in space. These organic molcules were not only identifed within our own Milky Way Galaxy, but also in other galaxies. So it looks like the existence of organic molecules is a universal phenomenon, and is driven by the energy from stars and the laws of chemistry.
There are two kinds of large biological molecules which form the basis of life on Earth, Proteins and Nucleic acids. Proteins are large molecules required for the structure, function, and regulation of the body's cells, tissues, and organs. Nucleic acids store the coded instructions for telling the cell machinery how to make proteins.
Proteins are made up of numerous molecular sub-units called amino acids. In fact half of the mass of all the biological material on Earth is amino acids. There are numerous amino acids, but all the proteins found in living things are made up of combinations of just 20 amino acids. Proteins are not found in the environment outside of living matter. Amino acids are. So we can't regard amino acids as 'life'. But when they combine to form proteins, it results in 'life'. Is it at this stage, the making of proteins out of amino acids, that non-life becomes life? Can we say that if you have the right combination of amino acids, you may be only one step away from 'life'?
So amino acids combine to form proteins. But where do the amino acids themselves come from? The English scientist Haldane suggested in the 1920s that not long after the formation and cooling down of the Earth, there was sufficient energy available from either the heat of the planet or even bolts of lightening to encourage chemical reactions between water and chemicals such as methane and ammonia which led to the formation of amino acids. This has been tested rigoursly in various laboratories across the world, and the results support this idea. Sealed vessels with various types of 'atmospheres' do produce amino acids when subjected to sources of energy such as electric discharges. And some of these amino acids belong to the 20 that are the building blocks of protein. But all the ingredients used to make these amino acids in the laboratory are also found in molecular clouds in outer space, where there is ample sources of energy from stars. So will we find amino acids in space? And if so, could some of the amino acids in space have made their journey to Earth to become the building blocks of proteins and ultimately life.
In 2003, NASA launched its fourth and final telescope in its 'Great Observatory' program. The Spitzer Space Telescope detects infrared energy with its state-of-the-art infrared spectrometer. It gathers data from its lofty perch in space which can not be detected by optical telescopes and is lost to ground based infrared detectors because of Earth's atmosphere.
It has made some fascinating discoveries such as in the constellation Ophiuchus. Here there is a young star system 375 light years from us called IRS 46, which consists of a huge cloud of gas and dust (dusty disks) swirling around a young star. It's basically a solar system in its early stages, a breeding ground for planets.
It's like looking back about five billion years in time at our own solar system. Eventually enough gas and dust will stick together with a good likelihood that planets will form, both gassy planets and rocky planets. 'Spitzer' has detected in the systems inner disc, the stars 'terrestrial' zone, hydrogen cyanide (HCN) and acetylene (C2H2), and carbon dioxide (CO2). Since the temperature of the molecules was established by the data from Spitzer, it was possible to position these molecules at this precise location from the star - the terrestrial or habitable zone. And we know from carrying out experiments in our laboratories that these molecules, in the presence of water, can form the ingredients of life's most essential components, some of the 20 amino acids and even 'adenine', one of the four chemical bases that make up DNA and RNA.
So, while we have not discovered amino acids, the building blocks of proteins (life) in the far off reaches of the universe, we have found the building blocks of amino acids.
Nucleic Acids are the other large biological molecule which forms the basis for life on Earth. These, like proteins, are long chain molecules made up of many sub-units strung together along a line. But the chemical sub-units in the nucleic acids are simpler than amino acids and there is less variety among them than there is among the twenty amino acids important for life. The basic building block for both DNA and RNA is a sugar molecule called ribose. And each sugar molecule is attached to one of five units called bases.
There are more than five bases, as there are more than twenty amino acids, but only five are used in the nucleic acids. The five bases are adenine (A), thymine (T), cytosine (C), guanine (G) and uracil (U). Only four of the five are found in each nucleic acid. DNA contain A, T, C and G. RNA contains A, U, C and G. The nucleic acids contain information (genetic information required to build life forms), and uses this four-letter alphabet to store and transmit this information. DNA stores the information. RNA helps translate this information to make amino acids and subsequently proteins.
So would we find sugar, the basic building block of the nucleic acids in space? Yes, in the year 2000 astronomers made the first discovery of a simple sugar molecule, glycolaldehyde, in a massive molecular cloud of gas and dust. It was detected by its faint radio emission using the 12 meter Kitt Peak radio telescope in Arizona. The molecular cloud is located 26,000 light-years away, near the centre of our Galaxy and called Sagittarius B2. The sugar molecule, Glycolaldehyde, is an eight-atom molecule composed of carbon, oxygen and hydrogen. It can form the more complex sugars, ribose, the spine of DNA and RNA as well as Glucose which is the sugar molecule found in fruits, when it reacts with other sugars or carbon molecules. Numerous different molecules have been found in Sagittarius B2, including glycine, a simple amino acid.
So it appears that the chemical precursors to life are formed in these massive molecular clouds long before planetery systems develop around stars. Not too long ago it was thought that these molecules required a terrestrial planet in a habitable zone of a star to enable there formation. So it seems much more work is required in theoritical and experimental chemistry to explain the now seemingly common identification of life molecules in space.
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