Life 1 – Origins and Chemistry
Chapter 15 - section 1, 2 & 4
In the Beginning..
The planets formed from the same cloud of gas and dust which gave birth to the Sun, about 4, 6
billion years ago..
Being made of the same stuff, the terrestrial planets likely looked very similar to one another at
The Earth has changed significantly since. But current conditions on Mars and Venus suggest
what the primordial Earth might have been like.
Earth’s original atmosphere probably looked a lot like those of Venus and Mars do today.
The gases likely to have been present include:
- Carbon Dioxide (CO2)
- Water (H2O)
- Hydrogen Sulfied
- Hydrochloric Acid
- Molecular Hydrogen
- Notice the absence of Oxygen
Origins of Life:
Every culture has a creation myth based on ancient myths, beliefs, and/or faith.
The accepted scientific view of our origins begins with the conditions on the newly-formed
The early environment likely featured
- An unpleasant atmosphere:
- Lots of ultra-violet (UV)
Urey Miller Experiment (1952): To reproduce the conditions believed to have existed on the Earth after its outer curst had
- H2, H2O, NH3, CH4 were combined in a flash:
- Electrical sparks in the flask simulated lightning.
After one week the flask contained a reddish brown muck.
This substance was found to contain
- Amino Acids (2%)
Amino acids are the building blocks of all known proteins.
Urey- Miller (Cont’d)
The experiment demonstrated that
- Organic molecules could be synthesized from inorganic ingredients without the presence
- Amino acids appear readily in the process
Our understanding of the Earth’s primordial environment has changed since 1952. But
the fundamental conclusion of the Urey Miller experiment has withstood the test of time.
Life was likely a natural outcome of the conditions which prevailed on Earth 4 billion
The first billion years witnessed slow but steady chemical evolution. However, exactly
how increasingly complex organic molecules combined to form living organisms is not
The ‘clumping” hypothesis process that increasingly large assemblies of organic
molecules formed at random. Those ‘clumps’ which were most adapt at processing
matter and energy became the first photocells.
But a prof of principle experiment is still awaited…
Chemical Basis of Life:
All known life forms are built up from organic molecules
Many of the organic molecules involved are gigantic. Such macromolecules involve
thousands of atoms and cone in four main types:
- Nuclear Acids (DNA, RNA)
- Carbohydrates (sugars)
- Lipids (fats)
All are polymers made up of chains of simpler molecules called monomers. Proteins:
Macromolecules composed of one or more polypeptides folded into a uniq