[meteorite-list] Did Comets Make Life On Earth Possible?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:20 2004
Message-ID: <200310022016.NAA17323_at_zagami.jpl.nasa.gov>

http://news.nationalgeographic.com/news/2003/10/1002_031002_cometstudy.html

Did Comets Make Life On Earth Possible?
Stefan Lovgren
National Geographic News
October 2, 2003

An ambitious new NASA research project aims to answer perhaps
the most vexing and profound of scientific mysteries: How did life on
Earth begin?

The multimillion-dollar undertaking, led by the NASA Goddard Space
Flight Center in Greenbelt, Maryland, brings together an
interdisciplinary team of scientists from around the world to study
how organic molecules are created in interstellar clouds and delivered
to planets as they form.

The research will focus on the role of comets. Many scientists believe
there is increasing evidence that comets supplied at least part of the
raw material for the origin of life on Earth. The theory is changing the
way scientists think about life in the universe and raises the
possibility of alien worlds.

"Our mission is to gain a greater understanding of the origin and
evolution of organic material on Earth," said Michael Mumma, a
comet expert and director of the Goddard Center for Astrobiology,
NASA Astrobiology Institute, who is leading the research. "The key
question is: Were water and organic molecules delivered to Earth by
cometary impact and does [that process] extend to planets
elsewhere?"

Dirty Snowballs

Astronomers believe that stars, planets, and comets form in a
massive chain reaction that begins when a cloud of interstellar
material collapses under its own gravity. Some of the material forms
the star-like our sun-and some of it gets spread out in a disk around
the nascent star.

Some material in this disk later aggregates and forms planets. Close
to the sun, where it's warm, leftover debris (rocky material) turns
into asteroids. In the outer regions, where it's cold, icy chunks of rock
and dust turn into comets.

It is generally believed that organic molecules, which contain carbon
atoms and are present in all life forms known to science, are trapped
in large amounts in both interstellar clouds and comets.

"We have extremely definite evidence from our radio observations
that there's quite an array of organic molecules in interstellar space,"
said Bill Irvine, a professor of astronomy at the University of
Massachusetts in Amherst, who is measuring radio waves from
celestial objects as part of the research effort.

There's other evidence that comets contain organic material. When
European spacecraft analyzed dust particles from the Halley comet in
1986, it turned out to be some of the most organic-rich material
measured in the solar system. Meteorites that have hit Earth contain
a whole suite of molecules, including amino acids, which play an
important role in terrestrial biology.

"If such material exists in meteorites, which come from a class of
asteroids, there's every reason to think it must also exist in comets,"
Irvine said.

Panspermia Goes Primordial

Most scientists have long believed that life on Earth began as a
"primordial soup" in a lake or pond some four billion years ago.
According to this theory, chemicals from the atmosphere combined
with some form of energy necessary to make amino acids-the
building blocks of proteins-to create the first primitive organisms,
kicking off the evolution of Earth's species.

But the primordial soup theory is being increasingly disputed. Many
geophysicists now say the Earth did not have enough gases, like
ammonia and methane, from which organic material like amino acids
could be produced.

Instead, a growing cadre of scientists believes the organic material
needed to create life may not have been produced on Earth, but was
instead brought here by comets. The newly formed Earth was likely
subjected to a fierce bombardment of comets four billion years ago.
These comets may have brought with them the organic compounds
that later evolved into living matter.

According to the most radical theory, known as "panspermia," life in a
ready-made form is ubiquitous in the galaxy and is brought by comets
to new planets. Few scientists subscribe to this hypothesis,
however.

Perhaps the main question is whether organic molecules can survive
space travel or if they break up and contribute the atoms that are
necessary to ultimately make biological material and water?

"Our museums contain examples of primitive meteorites that likely
are very similar to the material delivered by comets," said Mumma.
"The key point is that small bodies deliver their organics intact to
Earth's surface. This must have been a common event on the early
Earth."

Many scientists are now leaning toward a combination of the comet
impact theory and the primordial soup thesis. Some chemical building
blocks may have come from comets, but the assembly into life took
place on Earth.

"The comet impact theory fits in with the primordial soup theory,"
Mumma said. "They can be complimentary."

Drilling Into Comets

Scientists will measure the molecular make-up of comets to better
understand what chemical reactions formed them. This may provide
clues to the evolution of carbon-based chemistry on Earth in its early
history.

The new research will combine laboratory experiments, observations
with telescopes and spacecraft, and missions to sample comet and
asteroid material. A European mission not associated with NASA is
even going to land on a comet and drill into it as the comet journeys
toward the sun.

An important part of the project will focus on water, which is seen as
an essential ingredient of life. Scientists want to know if the Earth's
water was incorporated into the Earth as the planet formed or if the
water arrived on Earth as a result of cometary impacts after the Earth
was already formed.

"Earth's new oceans were filthy, and should have been full of organic
molecules and dust particles carried to our planet by comets and
primitive meteorites," said Mumma. "We want to learn how
significant their contribution was to the genesis of life on Earth."

The comet research could have a tremendous impact on the quest to
find life on other planets. After all, comets have slammed into many
other planets. If they supplied the raw material to form life on Earth,
what is to say the same thing hasn't happened on other planets?

One thing is for sure, however. Finding out exactly how life on Earth
began, and if it extends elsewhere, will take some time. The first
stage of the NASA project will last five years, but Mumma thinks it
could take as much as 25 years before scientists have a definite
answer about the origin of life on Earth.
Received on Thu 02 Oct 2003 04:16:55 PM PDT