Re: Paper: A Hazy View of Early Earth

On Oct 14, 10:31=A0am, "Robert Karl Stonjek" <rston...@xxxxxxxxxxxxxx>
wrote:
A Hazy View of Early Earth
October 12th, 2009 in Space & Earth / Earth Sciences
Haze in the early Earth atmosphere could have played a crucial role in th=
e
origin of life. By forming a protective shield, the haze would have
safeguarded organic substances from harmful ultraviolet (UV) radiation.

=93Knowing more about the atmospheric conditions right before life began =
to
develop could give researchers clues to how exactly life developed,=94 sa=
ys H.
Langley DeWitt of the Department of Chemistry and Biochemistry at the
University of Colorado at Boulder.

Many scientists believe hazy conditions existed on early Earth, and DeWit=
t
is the lead scientist of a new study investigating the effects of this ha=
ze.
The paper detailing this study was published in the June edition of the
journal Astrobiology.

Haze is produced when sunlight comes in contact with certain gases in the
atmosphere. The types of aerosols formed through this photochemical react=
ion
depend on the specific composition of the atmosphere.

The amount and the composition of the haze would determine whether it
produced a warming or cooling effect for the planet. This new study shows
that the amount of haze on early Earth was inadequate to have the type of
cooling effect that scientists had previously predicted.

Tips from Titan

Scientists have looked to Titan, Saturn=92s largest moon, to try to bette=
r
understand the organic haze that may have existed on early Earth. Titan h=
as
a thick atmosphere containing 95 percent nitrogen, three percent methane =
and
two percent of hydrogen and other hydrocarbons, and an atmospheric pressu=
re
about 1.6 times that of Earth. Titan is also the only planetary body othe=
r
than Earth with surface liquid (on Earth that surface liquid is water, wh=
ile
on Titan the surface liquid is ethane and methane.)

In a 2006 NASA study, a group of researchers that included DeWitt replica=
ted
the atmospheres of Titan and early Earth. They then compared the aerosols
produced in the laboratory to the haze observed in Titan=92s atmosphere d=
uring
NASA=92s Cassini mission. The group concluded that the two atmospheres we=
re
similar.

But there was one troubling result. An important distinction between the
atmospheres of Titan and Earth is the carbon dioxide that is present in t=
he
Earth=92s atmosphere. The laboratory results in the 2006 study suggested =
that
the reaction of carbon dioxide and methane would produce more haze on ear=
ly
Earth than the amount found on Titan. That implies that the Earth would h=
ave
been subjected to a large anti-greenhouse or cooling effect.

The current study puts that concern to rest. DeWitt and her colleagues di=
d
additional laboratory experiments that expanded upon the 2006 study. They
added hydrogen to the atmospheric composition and found that it reduced
aerosol formation to the point where any potential anti-greenhouse effect
would be negligible.

Mixing It Up
DeWitt=92s team also looked at how varying quantities of the three main
substances=97hydrogen, methane and carbon dioxide=97may have affected the=
haze
that formed on Earth billions of years ago.

=93Many models calculate the amount of haze that would be present at the
different ratios of these chemicals,=94 DeWitt explains. =93However, the =
models
don=92t always include experimental data in their calculations and instea=
d use
assumptions about the chemistry.=94

The new study used a simplified version of an atmospheric model to examin=
e
two scenarios. One mixture contained high quantities of hydrogen and carb=
on
dioxide with low amounts of methane. In the second simulation, the team
analyzed the effects of hydrogen in a mixture that contained high amounts=
of
methane. After the gas mixtures were exposed to UV radiation, the scienti=
sts
measured the aerosols that were formed.

Their findings showed that an increase in hydrogen levels reduced the haz=
e
formation rate. They also concluded that the amount of hydrogen present i=
n
the early Earth atmosphere most likely resulted in warmer surface
temperatures.

=93If an organic haze did form on early Earth, the consequences of its
presence beg all sorts of interesting questions,=94 says co-author Christ=
a
Hasenkopf of the Cooperative Institute for Research in Environmental
Sciences, also at the University of Colorado at Boulder.

A question for astrobiologists is what role haze would have played in the
formation of life. The scientists stated that the aerosols produced on ea=
rly
Earth provided a major source of organic substances to the Earth=92s surf=
ace.
Scientists think these organics played an important role in the origin of
life on our planet. Understanding the characteristics of haze that make a
planet=92s surface ripe for organic material could be immensely helpful i=
n the
quest for life on other planetary bodies.

Hasenkopf says some scientists believe that the early Earth atmosphere wa=
s
=93virtually oxygen-free when life first formed.=94 That allows astrobiol=
ogists
to think more broadly about what types of environments on other planets
could possibly support life.

=93We only know of one place in the entire universe that life was able to
initially form and develop, and that was on the early Earth,=94 says
Hasenkopf. =93The climactic conditions on early Earth provide clues to ou=
r own
origins.=94

Calculating Climate

Scientists don=92t know enough about our planet=92s environment approxima=
tely
four billion years ago to be able to precisely mimic the atmospheric
conditions back then. The laboratory re-creation of early Earth therefore
was based on many assumptions.

The study model used simplified calculations for determining surface
temperature, and the chemical reactions were based on shorter reaction ti=
mes
than what would have occurred under actual conditions. Additionally, the
researchers only focused on three gases: methane, carbon dioxide and
hydrogen. While these are believed to be the major constituents of the ea=
rly
Earth atmosphere, there could have been other components, such as sulfur
dioxide, which were not taken into account in this study. Still, DeWitt s=
ays
their study could improve the accuracy of models that predict chemical
reactions in the atmosphere.

Hasenkopf says the findings also can contribute to the understanding of t=
he
current effects of climate change.

Some scientists believe that the early Earth atmosphere contained higher
levels of carbon dioxide and methane than current atmospheric levels.
Hasenkopf explains that the interaction between the gases that produce
greenhouse warming and the haze that brings about the anti-greenhouse
cooling is similar to the present-day emissions caused by human activity.

=93On one hand, humans emit greenhouse gases, such as carbon dioxide, cau=
sing
warming,=94 Hasenkopf says. =93Yet humans also emit large amounts of part=
iculate
pollution, which may have a net cooling effect, similar to the early Eart=
h
haze.=94

Source: Astrobio.net, by Anuradha K. Herathhttp://www.physorg.com/news174=
587577.html

Posted by
Robert Karl Stonjek

There is a real catch 22 with UV. On one side it is really the only
major dependable source of energy
that covers all the earth. On the other hand it destroys life.
Well which is it - creates life or destroys it? It can't be both.
The only reasonable response I've seen is the idea of the Zinc World
(see other posts).

.

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