Transcript Origin of Life

Hydrothermal Vents
Primordial Soup & The Miller-Urey
Experiment
Life? From Space
What Can We Learn from Our Neighbors:
Life Elsewhere in the Solar System
The Ocean Floor: Site of Hydrothermal Vents
Deep-sea hydrothermal vents form along mid-ocean ridges, the
volcanic undersea mountain ranges where new seafloor is created.
MOR
http://maritime.haifa.ac.il/departm/lessons/ocean/lect07.html
Ocean Vents Around the World
Vents may be 3.5 - 4 billion years old,
but were discovered by scientists less
than 25 years ago (1977).
Deep-Sea Submersible Alvin
http://www.divediscover.whoi.edu/images/vent_sites.gif
http://oceanexplorer.noaa.gov/technology/subs/alvin/alvin.html
A hydrothermal vent is a hotspring/geyser on the seafloor. It
continuously spews super-hot (~400ºC), mineral-rich water
that helps support a diverse community of organisms.
black smoker
white smoker
Lush communities of strange and unique organisms survive
6-ft long tube worms
Microbes, some symbiotic,
combine vent chemicals with
oxygen and use the resultant
energy to make food and to grow.
Large animals populate the sulfide
mounds and the surrounding bare
lava, living on the energy
harnessed by the microbes.
ft long clams
Organisms that do not depend on photosynthesis or sunlight for energy!
http://www.ocean.udel.edu/deepsea/level-2/geology/vent.jpg
Tube worm
close-up
More Vent Organisms
Dense bacteria in vent waters
White crabs cluster near vents
Thousands of shrimp ~ 2430 m water depth on the
Central Indian Ridge
http://library.thinkquest.org/18828/media/snowblower.jpg
Instead of photosynthesis, vent ecosystems derive their energy
from chemicals in a process called "chemosynthesis."
Both methods involve an energy source (1), carbon dioxide (2),
and water to produce sugars (3).
Photosynthesis gives off oxygen gas as a byproduct, while
chemosynthesis produces sulfur (4).
Image courtesy Woods Hole Oceanographic Institution.
http://science.nasa.gov/headlines/y2001/ast13apr_1.htm
Supporters of this theory claim that the organic molecules at the
thermal vents are not formed in 300ºC temperatures, but rather in a
gradient formed between the hydrothermal vent water, and the
extremely cold water, 4ºC (39.2ºF), which surrounds the vent at the
bottom of the ocean.
The temperatures at this gradient would be suitable for organic
chemistry to occur.
Debates still remain, however, as to the gradient's effectiveness in
producing organic compounds.
http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/sites.html
Other Chemosynthetic Life in Methane-Sulfur Waters
•In cold, deep sea areas off Florida and Oregon coasts
•Similar communities of organisms get energy from methanesulfur-enriched waters
•Source is oil seeps not hydrothermal vents
•Both show that the Sun is not the ultimate energy source for
living systems.
Tube worms and crab, Gulf of Mexico
Tube worms and clams, Gulf of Mexico
http://www.gomr.mms.gov/homepg/regulate/environ/chemo/chemo.html
Could life have started in these hot deep sea
environments?
•Laboratory experiments simulating hydrothermal
vent conditions produced amino acids
•Later experiments: amino acids formed short
protein-like chains called peptides
•If only these peptides can replicate themselves and
form long chains = proteins, the basic substance of life!
•Some say they have generated self-replicating peptides or RNA
strands in the lab. But they fail to provide a natural source for
their compounds or an explanation for what fuels them.
But even if we find answers in lab experiments, will it be
the same as the Earth of 4 BILLION years ago?
Maybe not.
But the search continues…
The Primordial Soup Hypothesis
Oparin (Russian) and Haldane (British): independently
proposed similar hypothesis in the 1920s
reducing
atmosphere
(low oxygen)
=
+
abundant methane (CH4)
and ammonia (NH3)
ideal “primordial soup” for
the origin of life
1953: Stanley Miller, a grad student & his Nobel Prize-winning
adviser, Harold Urey set up this simple apparatus:
CH4
water vapor
(
(
)
electrode
NH3
H2
H2O
Ingredients:
Methane (CH4), ammonia (NH3) and hydrogen (H2) gas =
primitive atmosphere (note no oxygen)
Water boiled in a flask = primitive ocean
Electrodes attached to power supply to create a spark = lightning
Results of the Miller-Urey Experiment:
•After 1 week, the water in the flask turned into a
muddy brown liquid (the primordial soup)
containing amino acids, cyanide (HCN) and
formaldehyde (H2CO)
•Later experiments even produced 12 of the 20
most common amino acids needed for life!
•Abiotic synthesis of amino acids only needs a
source of chemicals and a reducing environment
Did Miller and Urey create life from
non-life?
• No. They were able to form amino acids which
are necessary ingredients for all life.
• Next step to life: transform amino acids to
proteins  sugars + nucleotide bases (adenine,
guanine, phosphate)  RNA or DNA (living cell)
• Numerous experiments and hypotheses on the
next step to life
• Still, others believe this path is not the way to
go. There must be some other way life began
on our planet.
Maybe the seeds of life on Earth came
from outer space…
Scientists have long believed meteorites and comets
played a role in the origin of life. Raining down on
Earth during the heavy bombardment period some 3.8
billion to 4.5 billion years ago, they brought with them
the materials that may have been critical for life, such
as oxygen, sulfur, hydrogen and nitrogen.
http://science.nasa.gov/headlines/y2001/ast20dec_1.htm
Astronomers have detected many kinds of organic molecules in
space, floating in clouds of gas or bound up in dust particles.
They range from the simplest - water, ammonia, methane,
hydrogen cyanide and alcohols, including ethyl alcohol - to more
complex molecules.
Interestingly, of the more than 70 amino acids found in
meteorites, only eight of them overlap with the group of 20 which
occur commonly as structural components of proteins found in
humans and all other life on Earth.
More Evidence:
December 20, 2001: A NASA scientist has discovered sugar and
several related organic compounds in two meteorites -- providing
the first evidence that another fundamental building block of life
on Earth might have come from outer space. Pass the sugar?
The carbonaceous Murchison meteorite, pictured here, harbors
sugar-related organic compounds.
Image copyright 2001 by New England Meteoritical Services
http://science.nasa.gov/headlines/y2001/ast20dec_1.htm
The prospects for life in the Universe just got
sweeter, with the first discovery of a simple sugar
molecule in space. The discovery of the sugar
molecule glycolaldehyde in a giant cloud of gas
and dust near the center of our own Milky Way
Galaxy was made by scientists using the National
Science Foundation's 12 Meter Telescope, a radio
telescope on Kitt Peak, Arizona.
http://www.aoc.nrao.edu/pr/sugar.html
In a related project conducted by members of
NASA's Astrobiology Institute, scientists have
created primitive organic cell-like structures.
They did it in their laboratory by duplicating the
harsh conditions of cold interstellar space! Did
comets carry such protocells to Earth?
http://science.msfc.nasa.gov/headlines/y2001/ast05apr_1.htm
ALH84001: The Martian Meteorite
In 1996, a meteorite was found in Allan Hills, Antarctica. Upon
examination, it was discovered that this meteor, which is 4.5 billion
years old, fell to the earth 13,000 years ago, and possibly contained
evidence of life on Mars. Inside the meteor, along tiny cracks,
scientists found evidence of what many believe to be ancient
bacteria. This is hotly debated.
http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/search.html