For Astrobiology, the class of meteorites that matters is Stony meteorites
WHY ?
The class “Stony Meteorites” contains several groups.
One of them is called CARBONACEOUS chondrites.
Chondrite= seed in Greek
Why do you think this name was chosen ?
Is Fe one of the main elements that life uses ?
What about Ni ?
Carbonaceous chondrites
Considered among the most primitive meteorites
➔
Dark gray to black
➔
Rich in C
➔Contain small spherical droplets of glass called chondrules
➔
Historical context
The first meteorite where organic carbon was found was Alais, a meteorite which fell in France in 1806.
Short after its fall, Thenard and Vauquelin, two French chemists, noticed that organic compounds were present in the rock. In 1834 the Swedish chemist Berzelius confirmed the
finding and started speculating about the origin and presence of these compounds beyond the Earth.
Berzelius took a piece of the meteorite and put it in water to
extract the organic compounds. He detected them by distillation
In 1858, Wöhler, German chemist and student of Berzelius, identified soluble carbonaceous molecules
in two other meteorites, named Kaba and Cold Bokkeveld. He concluded that the organics were produced by life. His statements show how strong were at that time the
ideas of the existence of extraterrestrial life. In 1868 French chemist Bethelot analyzed samples
of the Orgueil meteorite and found evidence of
hydrocarbons, carbonaceous molecules similar
to the ones found in petroleum.
Cold Bokkeveld
Many more meteorites fell in the century following these pioneering
analyses.
The Apollo sample return mission to the Moon enhanced the
development of new, more sophisticated analytical techniques and
instrumentation.
Lunar soil
In July 1969 the first Apollo mission (Apollo 11) returned samples that
were analyzed. Scientists became disappointed because they did not detect
any important bio­molecules in the lunar rocks.
However, the disappointment did not last too long...
Two months later, in September, the Murchison meteorite
would land on Australia
Using the newly developed state­of­the­art laboratory procedures
scientists could detect for the first time the precise nature of the
organic compounds in a meteorite. In particular, they detected
amino acids.
Many more analyses followed and as analytical techniques
became more accurate and improved, the analyses of several
types of meteorites and the implications of their results have been transforming the scientist's thoughts about the role of meteorites in the origin of life on Earth.
In the following slides we will study the different compounds found
in meteorites and their role in Astrobiology
What type of organic molecules have been detected
in meteorites ?
Two types of organic carbon:
Free soluble molecules
(usually water or solvent­soluble)
30­40% of the total carbon present
Insoluble macromolecules
(also known as kerogen­like)
60­70%
of the total carbon present
To isolate the kerogen from the rest of the rock, scientists
use strong acids that do not dissolve the organic molecules but
instead dissolve the rock.
This technique was originally developed
to study organic materials found in coal
and petroleum.
In meteorites, the kerogen­like material is mainly composed
of molecules called PAHs.
PAH stands for Polycyclic aromatic hydrocarbon
It is basically a huge molecule made of
multiple rings, or cycles, hence the name.
On Earth these molecules are found in wood burning gases and petroleum
Does that mean
that there is
petroleum in the
parent bodies of meteorites ?
It could mean that the same processes that make
PAHs on Earth operate in the early solar system
where PAHs were formed.
Which would be those processes?
For the petroleum we have
very high pressures and temperatures
In the wood burning we have
very high temperatures.
Where in the Universe do you find those conditions ?
How can PAHs be important for life ?
PAHs are not building blocks of life.
But when they get decomposed through chemical reactions,
they can be broken into smaller molecules which are
building blocks of life.
To isolate the free molecules, scientists make a powder
of the meteorite and dissolve it in water and a combination
of organic solvents (like acetone, alcohol, etc).
In meteorites, the soluble organic material is mainly composed
of molecules like amino acids and long carbon chains
In the meteorite Murchison, more than 72
different amino acids have been so far identified.
Which other molecules from the list below do you recognize as being building blocks of life ?
Do you remember why
amino acids were important for ?
How do we know that the compounds are ET ?
1 Isotope ratios
2 Presence of unique compounds that
are absent on the Earth (like some amino acids)
Alpha­isobutyric acid, isovaline 3 Presence of “mirror­image” (isomers) molecules
What are isotopes ?
15
N/ N=3.7x10
14
18
­3
O/16O=2 x10­3 in ocean water
in air
these ratios vary in natural materials
by up to 10%
Other interesting observations related to the carbon of some meteorites
is that the carbonaceous material is sometimes found in phases with unique shapes
that we call carbon globules.
Organic globule in Murchison
Organic globule in Orgueil
Organic globule in Orgueil
C
N
O
Show also isotopic images
These globules are
organic
Meteorites can contribute to the origin of life on the early Earth with
two types of carbon: organic molecules that can be incorporated early in the origin of life on Earth and carbonaceous globules which can actually be places where chemical reactions occur and that might enhance the formation of the first cell.
individual organic molecules
organic globules where reactions can occur
Summary of the types and amounts of organic
molecules that have been identified in meteorites
and their link to astrobiology
Molecule type
Concentration (ppm)
Function for life
60
Building blocks of proteins
Aliphatic hydrocarbons
35
Precursors of fatty acids
Aromatic hydrocarbons
3300
Purines and pyrimidines
1.3
Backbone of DNA
38
Metabolism
Amino acids
Alcohols, aldehydes and ketones
Phosphonic acids
2
Precursors of aliphatic chains
Energy and backbone of DNA
Link between meteorites and astrobiology
Most meteorites originate from asteroids
A fraction of them contains
organic molecules
During the heavy bombardment period, big chunks of asteroids were hitting the Earth. These objects would have nourished the Earth with organic molecules
Most of these organic molecules are
building blocks of life
Meteorites
Delivered some of the bricks to form life
Analytical techniques to investigate the organic materials in meteorites
Electron microscopy (EELS and EDX)
●Raman spectroscopy
●X-ray spectroscopy
●Infrared spectroscopy
●Nuclear microprobe
●Ion microprobe
●Gas and Liquid chromatography
●
ELECTRON MICROSCOPY=MEASURES ELEMENT SPACE DISTRIBUTION
AND ABUNDANCE
EDX
EELS
ION MICROPROBE=MEASURES ISOTOPES
Isotope space distribution and abundance and their ratios
RAMAN SPECTROSCOPY=MESURES THE TYPE OF
BONDING IN THE MOLECULE
100
90
80
70
60
50
40
1000
1500
2000
2500
3000
X-RAY MICROSCOPE=DETECTS
THE SPACE DISTRIBUTIO OF
ELEMENTS AND THEIR BONDING
STATE
INFRARED SPECTROSCOPY=
DETECTS BONDING STATE OF
MOLECULES
GAS CHROMATOGRAPH
LIQUID
CHROMATOGRAPH
CHROMATOGRAPHY=DETECTS TYPE OF MOLECULES
NUCLEAR MICROPROBE=DETECTS ABUNDANCE OF LIGHT
ELEMENTS AND DEPTH DISTRIBUTION