Geologists Uncover New Evidence About the Rise of Oxygen on Earth(Forwarded)

Media Relations
Caltech

Contact:
Robert Tindol, (626) 395-3631

October 24, 2005

Geologists Uncover New Evidence About the Rise of Oxygen

PASADENA, Calif. -- Scientists believe that oxygen first showed up in
the atmosphere about 2.7 billion years ago. They think it was put there
by a one-celled organism called "cyanobacteria," which had recently
become the first living thing on Earth to make oxygen from water and
sunlight.

The rock record provides a good bit of evidence that this is so. But one
of these rocks has just gotten a great deal more slippery, so to speak.

In an article appearing in the Geological Society of America's journal
Geology, investigators from the California Institute of Technology, the
University of Tübingen in Germany, and the University of Alberta
describe their new findings about the origin of the mineral deposits
known as banded-iron formations, or "BIFs." A rather attractive mineral
that is often cut and polished for paperweights and other decorative
items, a BIF typically has alternating bands of iron oxide and silica.
How the iron got into the BIFs to begin with is thought to be a key to
knowing when molecular oxygen first was produced on Earth.

The researchers show that purple bacteria -- primitive organisms that
have thrived on Earth without producing oxygen since before
cyanobacteria first evolved -- could also have laid down the iron oxide
deposits that make up BIFs. Further, the research shows that the newer
cyanobacteria, which suddenly evolved the ability to make oxygen through
photosynthesis, could have even been floating around when the purple
bacteria were making the iron oxides in the BIFs.

"The question is what made the BIFs," says Dianne Newman, who is
associate professor of geobiology and environmental science and
engineering at Caltech and an investigator with the Howard Hughes
Medical Institute. "BIFs are thought to record the history of the rise
of oxygen on Earth, but this may not be true for all of them."

The classical view of how the BIFs were made is that cyanobacteria began
putting oxygen in the atmosphere about 2.7 billion years ago. At the
same time, hydrothermal sources beneath the ocean floors caused ferrous
iron (that is, "nonrusted" iron) to rise in the water. This iron then
reacted with the new oxygen in the atmosphere, which caused the iron to
change into ferric iron. In other words, the iron literally "rusted" at
the surface of the ocean waters, and then ultimately settled on the
ocean floor as sediments of hematite (Fe2O3) and magnetite (Fe3O4).

The problem with this scenario was that scientists in Germany about 10
years ago discovered a way that the more ancient purple bacteria could
oxidize iron without oxygen. Instead, these anaerobic bacteria could
have used a photosynthetic process in which light and carbon dioxide are
used to turn the ferrous iron into ferric iron, throwing the mechanism
of BIF formation into question.

Newman's postdoctoral researcher Andreas Kappler (now an assistant
professor at the University of Tübingen) expanded on this discovery by
doing some lab experiments to measure the rate at which purple bacteria
could form ferric iron under light conditions relevant for different
depths within the ocean.

Kappler's results showed that iron could indeed have been oxidized by
these bacteria, in amounts matching what would have been necessary to
form one of the Precambrian iron deposits in Australia.

Another of the paper's Caltech authors, Claudia Pasquero, determined the
thickness of the purple bacterial layer that would have been needed for
complete iron oxidation. Her results showed that the thickness of the
bacterial layer could have been on the order of 17 meters, below wave
base, which compares favorably to what is seen today in stratified water
bodies such as the Black Sea.

Also, the results show that, in principle, the purple bacteria could
have oxidized all the iron seen in the BIFs, even if the cyanobacteria
had been present in overlying waters.

However, Newman says that the rock record contains various other kinds
of evidence that oxygen was indeed absent in the atmosphere earlier than
2.7 billion years ago. Therefore, the goal of better understanding the
history of the rise of oxygen could come down to finding out if there
are subtle differences between BIFs that could have been produced by
cyanobacteria and/or purple bacteria. And to do this, it's best to look
at the biology of the organisms.

"The hope is that we'll be able to find out whether some organic
compound is absolutely necessary for anaerobic anoxygenic photosynthesis
to occur," Newman says. "If we can know how they work in detail, then
maybe we'll be fortunate enough to find one molecule really necessary."

A good candidate is an organic molecule with high geological
preservation potential that would have existed in the purple bacteria
three billion years ago and still exists today. If the Newman team could
find such a molecule that is definitely involved in the changing of iron
to iron oxide, and is not present in cyanobacteria, then some of the
enigmas of oxygen on the ancient earth would be solved.

"The goals are to get at the types of biomolecules essential for
different types of photosynthesis -- hopefully, one that is
preservable," Newman says.

"I guess one interesting thing from our findings is that you can get
rust without oxygen, but this is also about the history of metabolic
evolution, and the ability to use ancient rock to investigate the
history of life."

Better understanding microbial metabolism could also be of use in NASA's
ambitious goal of looking for life on other worlds. The question of
which organisms made the BIFs on Earth, therefore, could be useful for
astrobiologists who may someday find evidence in rock records elsewhere.

Andrew Yee wrote:
Media Relations
Caltech

Contact:
Robert Tindol, (626) 395-3631

October 24, 2005

Geologists Uncover New Evidence About the Rise of Oxygen

PASADENA, Calif. -- Scientists believe that oxygen first showed up in
the atmosphere about 2.7 billion years ago. They think it was put there
by a one-celled organism called "cyanobacteria," which had recently
become the first living thing on Earth to make oxygen from water and
sunlight.

So what happened to the H2?
Was it combined with carbon to form the hydrocarbons which run the car
today?

Jim G

wrote:
Andrew Yee wrote:
Media Relations
Caltech

Contact:
Robert Tindol, (626) 395-3631

October 24, 2005

Geologists Uncover New Evidence About the Rise of Oxygen

PASADENA, Calif. -- Scientists believe that oxygen first showed up in
the atmosphere about 2.7 billion years ago. They think it was put there
by a one-celled organism called "cyanobacteria," which had recently
become the first living thing on Earth to make oxygen from water and
sunlight.

So what happened to the H2?

Escaped into space.
http://66.102.7.104/search?q=cache:z...Earth%22&hl=en
John Curtis

On 27 Oct 2005 08:09:55 -0700, John Curtis wrote:

|
wrote:
| Andrew Yee wrote:
| Media Relations
| Caltech
|
| Contact:
| Robert Tindol, (626) 395-3631
|
| October 24, 2005
|
| Geologists Uncover New Evidence About the Rise of Oxygen
|
| PASADENA, Calif. -- Scientists believe that oxygen first showed up in
| the atmosphere about 2.7 billion years ago. They think it was put there
| by a one-celled organism called "cyanobacteria," which had recently
| become the first living thing on Earth to make oxygen from water and
| sunlight.
|
| So what happened to the H2?
|
|Escaped into space.
|http://66.102.7.104/search?q=cache:z...Earth%22&hl=en
|John Curtis

Wrong. In photosynthesis the hydrogen obtained from water is incorporated
into organic matter.

You are thinking of the H2 produced from ultraviolet dissocation of water.

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