the 1920's scientists Oparin
and Haldane theorized that given a planet like the early
Earth, with a reducing atmosphere (ie one with no oxygen), high
UV radiation, and the basic chemical elements, then it might be
possible to create organic molecules from inorganic precursors.
In 1953 Miller
tested their predecessors' ideas with a famous experiment that
they said simulated those conditions. Sure enough it worked.
They mixed water vapor, hydrogen, methane and ammonia and passed
high-energy electrical discharges through the "soup". Within
a few days they had made several organic compounds and amino acids
- the building blocks of life. The experiments were modified
and repeated and many chemicals, including all the twenty amino
sugars and the purine and
pyramid-like bases of nucleic acids. If oxygen gas
was added, however, the processes failed.
the experiment, which is now sometimes repeated in school laboratories,
did show that the basic organic compounds that are necessary building
blocks for life could be easily synthesized from elementary materials
and "natural" conditions. Having the building blocks, though,
is a long way from having the building! Imagine the building blocks
of life as a tub of Lego parts, with life itself represented by
a model that you may be able to build from the parts - a dune-buggy,
make the dune-buggy you need to undertake a series of very precise
steps selecting parts in the right order, orientating them, and
then slotting them into place. Creating a living entity is
a similar process, as far as we understand. But we only have
a vague idea of how to fit the parts together, at least from first
principles. All we are able to do is the equivalent of shaking
the tub of Lego and tipping it out on the floor, hoping a dune-buggy
may spontaneously appear. And how likely is that? There
is virtually no chance at all.
nature, there is a solution to the dune-buggy problem. It
is DNA. The DNA is both the
plan and the means of issuing orders to make the "dune-buggy"
of life. But take away the instructions and nature
is back to "tipping the tub", just as it was before the
first life appeared. The big mystery of life is not how
it is assembled, but how did the first set of assembly instructions
come into being, apparently in a dumb Universe without intelligent
the initial euphoria, the Miller-Urey experiment took us no further
than repeating that very question in our quest to understand how
life came about. It was, and remains, a long way from giving
us the answer to the origin of life and the means to create it
from first principles.
the 1980's ideas about the early Earth had changed and the Miller-Urey
experiment was considered irrelevant. It no longer represented
the conditions of the early Earth, according to the new theories.
However now Miller and Urey's experiment is being revived, not
in its original form, but in a form that mimics conditions that
are thought to exist in deep space.
from Deep Space
Members of the Laboratory Astrophysics Group, at NASA Ames, are
researching the origins of life in deep space: the team
and some of their apparatus. © NASA,
work by a team
of scientists led by Lou
Allamandola at NASA Ames Research Center at San Jose, has
shown how such compounds may form from basic elements and molecules
in interstellar space. He and his colleagues
created a vacuum chamber, cooled it to a very low temperature
of 10 K above absolute zero - typical of interstellar space -
and released into it some minute gaseous quantities of water,
hydrogen, nitrogen, oxygen, and carbon-monoxide, along with some
grains of sand - SiO2.
coronene (C24H12) Molecule - One of the molecules
produced. © NASA, 1999
They bombarded this with ultraviolet light and to their amazement,
within a short time new and complex chemicals had formed around
the silicate grains. These included ketones, formaldehyde,
polycyclic aromatic hydrocarbons
(PAH), ammonia, methane,
methanol, alchohols of various kinds, poly-oxymethylenes and dozens
of other highly complex organic chemicals - some of which were unknown
and had no name!
was most surprising, though, was the fact that the chemical residues
formed into vesicles similar to those found in the Murchison
meteorite by David
Deamer. The vesicles created in the vacuum chamber
have some interesting and significant characteristics. One
end is hydrophilic and the other end is hydrophobic - they
both love and hate water! This enables molecules to
be self-organizing in the presence of water and this ability, or
characteristic, is a simple sorting process that may go some way
towards understanding how life could self-organize, without some
intelligent presence overseeing its assembly. In fact
behaves like a lipid,
which is a fatty or oily bio- (rather than just an organic) molecule
that is a major component in living cells and serves a variety of
most important of these functions is the creation of a boundary,
enclosure or membrane, that isolates whatever is inside
from the harsh and potentially destructive Universe outside.
Surrounding and isolating a cocktail of potentially life-making
chemicals in this way, where they can carry out their processes
without external perturbations, must be vitally important if life
is to "get started". If it is possible for lipids
to form from "raw", inorganic chemicals, by simple processes that
would be common in space, then a major factor in understanding
the origins of life has been discovered.
is a step closer, towards self-assembling our "dune-buggy" of
life. We now tip the parts out on to a tray, they
now remain together, half of them no longer roll away across the
floor to get lost or trodden on! But it is still a
long way from a complete buggy. If we take a logical approach,
though, we might finally assemble the buggy by putting sub-assemblies
together - wheels, engines, chassis. The final buggy is
then made from a few sub-assemblies. Did life happen by
the same process? If so how did the subassemblies self-assemble?
Could it have been by natural physical
processes that create structure? We can see this happening throughout
the non-living world. Spheres form from liquid in free-fall.
Tornadoes (Twisters) are helical in structure, like DNA.
Crystals form amazing geometric shapes. All these are a
form of structure and assembly. They are just three examples
and there are many more. Can you think of any?
back in the space simulation chamber, further development of the
chemicals continued as the experiment progressed. Compounds
known as quinones and alkaloids
developed from the PAH's. Alkaloids are common
in plants, where they play a crucial role in many aspects of a
plant's life. Quinones assist in the electrons' mobility
inside living cells. They are used in photosynthesis
in plants and bacteria, and in animal cells where they become
muscle and brain "food".
is becoming clear that life precursors could be created in space,
from the simplest of chemicals and in the most unpromising of
conditions. The question that now occurs is this:
did life start in space, or was it that the chemical precursors
of life could form in space and rain down on the planet as comets
and other space debris?
second option is quite likely, but the true origin of the first
living cell is still as elusive as ever. But major breakthroughs
happened in the last decade of the last millennium and perhaps
the answers to our fundamental questions about life will be answered
Allamandola © NASA, 1999
The team at NASA Ames are hopeful that perhaps they are only a short
step from seeing life spontaneously come into existence. As
Dr Allamandola says: " When I see this kind of complexity forming
under exceedingly simple conditions, I begin to really believe that
life is a cosmic imperative." The full story is at Life
from a dirty snowball.
in Calcutta, India, a team at the S N Bose National Centre
for Basic Science has produced a mathematical model of how chemicals
would evolve in a large cloud of interstellar dust and gas 7 light-years
across which is collapsing under its own gravity. The
cloud contained 12 elements, including Hydrogen, Carbon and Nitrogen.
and it contracted for a million years. The simulation resulted
in the production of Anadine, which is one of the bases for DNA.
The full story is at Seeds
is another step closer to building the buggy!
take the Life in Space Knowledge Challenge
organic molecules form quickly in old stars
Implications for the Origin of Life-chemical synthesis in the circumstellar
Thursday Classroom - Life on the Edge
Deamer - article
Deamer - personal
- making vesicles
- a vesicle
Dr. Louis Allamandola
Welcome to the Astrochemistry
Lab - PAH Dust Ice
1999 Satellite Events Enterprises Inc.