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News Story: "Your Ancestors May Be Martian"
"Your Ancestors May Be Martian"
By Michael Paine
Special to space.com News
Nov 08 1999 09:58:35 ET
Suppose that billions of years ago life developed on Mars.
Primitive, tiny organisms thrived deep within
rocks and made a living from water and
chemicals seeping through those rocks.
Now imagine that a huge asteroid collided with Mars. Millions of
Martian rock fragments were thrown into
space by the force of the impact. Tough Martian organisms
hitchhiked on some of these rocks. Many
rocks went into orbit
around the Sun, and, after hundreds of thousands of years some of
these collided with the Earth, and a
few rocks reached the surface. Some hardy
Martian organisms survived the journey, colonized the Earth and
eventually evolved into the huge variety of
life that we know today.
Just a few years ago this scenario would have been dismissed as
wildly imaginative and impossible. It is
still highly speculative, but recent discoveries in several fields
of science have shown that it is far from
impossible -- our
ancient ancestors might have been Martians.
Enter the nanobes:
It is not every day that a scientist discovers a possible new life
form. Dr. Phillipa Uwins works in the Center
for Microscopy and Microanalysis at Queensland University,
Australia. Last year she was asked to analyze
some
rock samples taken from several miles under the seabed in a
drilling operation off the coast of western
Australia. The temperature at this location was around 300
Fahrenheit (150 C) and the pressure was an
incredible 2,000 times normal atmospheric pressure at sea level.
During an electron microscope examination, Uwins found what
appeared to be tiny, dormant organisms
only 20 nanometers across (a nanometer is one
-billionth billionth of a meter). She named them "nanobes."
To Uwins' surprise, filaments grew when samples of the nanobes
were given some food and exposed to
normal temperatures and pressures. She was also
surprised because the cell walls of the nanobes survived the
intense radiation and vacuum of the electron
microscope.
Uwins teamed up with two microbiologists to further investigate
the nanobes. A range of chemical tests
indicated that the tiny objects contained DNA. This finding
challenged the notion that a "cell" 20
nanometers in diameter was too
small to have room for this essential ingredient of life as we
know it (it is also one of the arguments against
the "nanofossils" in Martian meteorites --discussed below).
Here was a tough little critter that was able to survive the heat
and pressure deep underground and,
possibly, the vacuum and radiation of an electron microscope. The
Queensland team may have found an
organism that can survive a ride between the planets aboard a
meteorite.
Creatures don't have to be as small as nanobes to survive
space-like conditions. Several other examples
of "extremophiles" (organisms that can
survive very hostile conditions) have been found by other
researchers in recent years, including bacteria
that live inside nuclear reactors.
Meteorites from Mars:
Rocks from Mars have made it to the Earth. Remember the fuss in
1996 when NASA scientists claimed
they had found possible fossil evidence of
ancient life in a meteorite from Mars? (That debate is still not
settled.)
After being blasted from the surface of Mars, one small chunk of
rock spent 16 million years in orbit around
the Sun. Then some 13,000 years ago it collided with the Earth and
landed on the icy Antarctic. In 1984,
scientists searching for meteorites found it and named it
ALH84001. Ten years later researchers figured
out that ALH84001 had come from Mars. This was based partly on an
analysis of the Martian atmosphere
by the Viking spacecraft in 1977 -- but that is another detective
story.
A dozen or so other meteorites are now known to come from Mars. In
1911 one of them fell to Earth in
Egypt and killed a dog, after which it took almost 80 years to
recognize that the unlucky dog had been
killed by a rock thrown from Mars. Planetary scientist and crater
expert Dr. Jay Melosh, from the University
of Arizona, has estimated that about half a ton of Martian
material falls to Earth each year.
Melosh observed that some of the Martian meteorites had no
evidence of a violent shock when they were
blasted into space from the surface of Mars.
This meant "back to the drawing board" for theories about rocks
ejected into space by impacts -- they
were supposed to be partly melted by the intense heat from the
shock wave. Melosh worked out that rocks
near the surface could be launched into space without "shock
heating." The effect is
something like crumbs being flicked from a shaken picnic blanket.
The discovery meant that organisms hiding within ejected rocks
could survive the blast from a nearby
asteroid impact. There are, however, many other hazards in a
flight from Mars to Earth. Melosh
investigated these hazards and was able to show that some
organisms had a fighting chance of making
the trip between the planets.
Surviving space flight:
In his classic 1865 novel 'From the Earth to the Moon,' science
fiction writer Jules Verne wrote of a piloted
space capsule being launched by a gigantic cannon. Verne was aware
of the scientific error with this idea
-- the astronauts would be crushed by forces thousands of times
greater than the pull of gravity(1 G or an
increase in speed of 32 feet per second every second). Verne knew
that the steady and comparatively
gentle rocket was the way to reach space, but his audience of the
day was more likely to believe the
cannon story.
For most creatures on Earth, exposure to several hundred Gs would
be fatal. They have no hope of
surviving the Jules Verne cannon blast, or a ride on a rock
blasted into space by an asteroid impact. But
some very primitive forms of life are so small and simple that
they can survive enormous
accelerations--10,000 G or more.
One way that scientists can test the ability of organisms to
survive very high G forces is to fire them out of
a cannon. This was recently done in Sweden and a substantial
proportion of dormant organisms survived
the launch conditions. Jules Verne had the right idea but the
wrong organism.
Of all the rocks blasted from the surface of Mars into orbit
around the Sun, about 1 in 15 will eventually
collide with the Earth. Some make it in
thousands of years. Others may take millions of years. For
organisms aboard these rocks the journey
would be extremely hazardous, with freezing temperatures, deadly
cosmic rays and ultraviolet radiation.
But the rock spaceship provides some protection from radiation and
cosmic rays, and the deep freeze
may actually help some organisms survive the tough conditions.
Next, the organisms would have to survive the rigors of colliding
with the Earth. The outside of a meteorite
glows white-hot as it plunges into the
atmosphere at 25,000 mph or more. Many burn up completely and
never reach the ground. However, a
small percentage survive and fall to the surface.
The inside of a meteorite is protected from the heat of re-entry
because rock is a very good heat insulator.
People who have come across a freshly fallen meteorite sometimes
report that a layer of frost has formed
on its surface.
The inside remained at the freezing temperature of space even
though the outside glowed white hot during
entry. Any organisms within the meteorite could therefore, in
theory, survive to reach the surface of the
Earth.
Finally, the organisms would have to make a home for themselves on
their new planet. Billions of years
ago the conditions on Earth might have been similar to those on
Mars, so colonizing the Earth may not
have been difficult,compared with the hazards of getting there.
Of course, this scenario all depends on Mars having some tough
forms of microscopic life billions of years
ago. Maybe the exciting space missions to Mars planned over the
next few years tell us whether this was
the case or not.
Lifeboats in space:
Another intriguing possibility is that meteorites may have acted
as lifeboats ("escape pods" for Star Wars
fans). Giant asteroids and comets bombarded the planets up until
the time that life
is first thought to have arisen. Following some of these impacts
the surface of the Earth would have been
sterilized by temperatures much hotter than an oven, and any
oceans would have boiled away. Perhaps
the only escape for organisms was to be blasted into space and the
really lucky ones returned to the Earth
when things cooled down. The same rescue system could have worked
for any life on Mars.
Maybe Martians came from Earth:
Even if the scenario of Mars life seeding the Earth is not
correct, the reverse seems quite likely. Rocks all
over the surface of the Earth have been found to contain
microscopic life. It is hard to find places that don't
have life. Hundreds
of huge asteroid impacts have occurred on Earth since life first
began.
Without doubt some of these impacts would have launched rocks
bearing microscopic life.
In his book "The Fifth Miracle," physicist Paul Davies discusses
the origins and development of life on
Earth. He pays great attention to the possibility of life being
exchanged between Earth and Mars and
concludes "It is therefore inevitable that life from Earth has
reached Mars ... that is why I am certain that
there was life on Mars in the past, and may well be life there
today".
Paul Davies also notes that, 4 billion years ago, Mars may have
been more suitable than Earth for the
development of life. He argues that we should be prepared for the
possibility, remote though it may seem,
that we are descended from Martians.
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