Life in the Beginning

What is Life

Carbon

When Did Life First Appear on Earth

How did Life First Appear

The First Inhabitants

Building blocks of life are in space

Essential Elements of Life

Window of Opportunity has increased

Panspermia, Comets the Galactic Taxis

Essential Elements Of Life
It seems life makes extensive use of the four most common reactive elements that exist; carbon, hydrogen, oxygen and nitrogen. Other elements are present in the molecules of life, but in much smaller quantities as we would expect from their relative scarcity in the environment.

Carbon is very common in the universe. Why is this? From stellar nucleosynthesis - the creation of heavier elements from lighter elements - we know that carbon 'burning' only takes place in stars that have more than eight times as much mass as the sun. And about 95 percent of all stars have less mass than this. So in 95 percent of stars, the triple-alpha process dominates, which is the fusion process where three Helium nuclei are turned into Carbon. So nuclear fusion in their interiors never gets further than this fusion of helium nuclei to make carbon nuclei.

And our knowledge of stellar evolution tells us that stars with masses of one to eight times the sun's mass (stars where no carbon-burning takes place), will evolve and end up in what's called the Asymptotic Giant Branch (AGB). And at a certain stage in the life cycle of these type of stars, the star expands to become a red giant. Carbon made in the core of a star is carried up to the surface by convection and builds up in outer layers of the star. As the star expands further, the gravity holding the outer layers gets weaker and is eventually overcome by the outward radiation pressure. And this essentail material for life, carbon, escapes from the surface of the star in a stellar wind thereby explaining the relative abundance of carbon in the universe.

In fact because of the low temperatures of the escaping materials many simple organic molecules can form. Over 60 of these kinds of molecules have been detected in the spectra of these AGB stars by space based infrared satellite observatories.

Phosphorus is also vital to life which is an exception in the sense that it turns up in surprising amounts in the molecules of life despite it's relative rarity. It is the fifth most important biological element in terms of mass. And the reason for this is that it behaves in a strange way due to a 'quirk' at the quantum mechanics level which sometimes allows it to make bonds with five other atoms at the same time. So its ability to form many chemical bonds more than makes up for its relative scarcity in the environment.

Phosphorus is essential to life, because it is essential to adenosine triphosphate (ATP), the main usable energy source found in all living things. ATP is both an energy-providing and energy-storing molecule. It is vital for metabolism and most cell activities.

We see phosphorus in meteorites. So did meteorites provide the phorphorus for life on Earth? Or since molecules containing phorphorus appear to be abundant in space did life itself start out there? There is also much evidence from simple experiments on meteorites carried out in the University of Arizona in 2004, based on minerals found in meteorites and water, which produced a variety of phosphorous compounds, including one similar to ATP, which is critical as we said for all life by providing energy for cells.

Chirality: We also see another link between the molecules of life on Earth and molecules found in meteorites. Amino acids and certain sugars can exist in both left-handed or right-handed forms. The handedness, or chirality, is defined by the way the molecules are affected by polarized light. But life on Earth uses almost exclusively left-handed amino acids to build proteins, and right-handed sugars to build nucleic acids. No one knows why this preference developed in living systems. And as this is the way all life on Earth is today, it strongly suggests that all life descended from a common ancestor that also had this chirality.

And now astronomers have discovered that amino acids found in meteorites, the left-over debris from the early solar system, are also left-handed. So it seems this asymmetry existed in the molecules of life in regions of the Solar System and beyond before the Earth was even formed. Surely this implies that left-handed amino acids seeded the Earth in greater numbers than right-handed amino acids, as this is the only viable explanation as to why amino acids in the molecules of life are left-handed.