THE ORIGIN OF LIFESC
IEN
CE
PH
OT
O^ L
IBR
AR
Y
Computer
visualisation of
biomolecules
in the Universeultraviolet light or lightning, could
be conducive to the production of
complex organic molecules, they
said. Finally, at some point, fat-like
molecules could have formed an
‘oily film’ on the soup that enclosed
important molecules within bubbles,
forming the first cell-like units.
For decades, however, there was
ver y little evidence to suppor t t his
idea. It appeared that the essential
molecules of life – proteins, fat-based
cell membranes, and DNA – were only
found in living organisms and could
not form without the molecular
machinery contained inside cells.
In 1952, a young scientist named
Stanley Miller put water, methane,
hydrogen and ammonia together, and
f razzled it wit h t housa nds of volts to
emulate the fierce electrical storms
that would have been a feature of
Earth’s turbulent atmosphere at the
time life f irst appea red (see ‘The
Key Experiment’, left).
Within a few days, the mixture
had turned into a rich, brown mix
of chemicals and analysis found that
amino acids – the building blocks of
proteins – had formed spontaneously.
The experiment was key in
supporting the view that life could
arise from simple chemicals on the
surface of the Earth. Modern analysis
has since found that all 22 of thecatalyse reactions, just like iron- and
sulphur-based proteins do in modern
cells. Today, such vents often host
complex microbial communities,
fuelled by the chemicals dissolved in
the vent fluids.
The most exciting aspect of t his
theory, however, is the complex
chemistry occurring between the
inside and the outside of the
microscopic pores. This could create
what is known as a ‘proton gradient’ –
an absolutely key part of the way all
organisms store energy and use it to
build complex molecules.
The final stage in the theory again
involves the production of fatty
molecules, which can spontaneously
form bubble-like, cell-like spheres.
Having been produced in t he chemical
froth, some of these bubbles could
have enclosed self-replicating sets of
molecules – forming the very first
organic protocells.Could life have arrived on
Earth from space?
The idea that life originated in
space, known as panspermia, is
not as wacky as it sounds. Scientists
have found lots of unexpectedly
complex molecules, such as amino
acids or small components of DNA,
nestled on comets or meteorites that
have crashed to Earth. 5essential amino acids required for
life can be made like this. Scientists
have also since made other important
biological chemicals in similar ways,
such as nucleotides, the building
blocks of DNA.
So did life for m in t he primordial
soup? Well, this approach only gets
us so fa r. Even wit h a ‘soup’ stocked
with the ingredients of life, such as
amino acids and nucleotides, it’s still
enormously difficult to get these
ingredients to for m ver y complex
biochemicals, such as proteins or
DNA. And it’s even more diff icult
to ma ke versions of t hose molecules
with meaningful biological functions.Q
Could life have begun
anywhere else?A
Another theory gaining
credibility is the idea that life
began in deep-sea hydrothermal vents.
At the time of life’s origin, the seawater
was acidic and positively charged. In
contrast, the vents ejected negatively
charged, alkaline substances.
These fissures in the Earth’s crust,
where alkaline minerals reacted with
acidic seawater, created tiny pores in
rocks, which appea r to concent rate
chemicals produced by other reactions
in the vent.
Iron- and sulphur-based minerals
in the vents could have helpedQ
A