PPT Slide
Is there evidence from meteorites?
Found December, 1984 in Antarctica.
Weighs 1.93 Kg (4.75 pounds)
Seems to be: The gas trapped in the meteorite is of the same composition as the Martian atmosphere - a fingerprint.
The only process that can supply this much energy is
meteoric impact: Need 1/2 - 2 km diameter.
Volcanoes are incapable of doing this.
Initially in orbit around Mars
Orbit perturbed by Mars and Jupiter
Hit Earth by chance ~ 13,000 yrs. ago
PPT Slide
Martian meteorite ALH 84001 at Johnson Space Center, after being returned from Antarctica. For scale, the black cube is 1 cm on a side. The outside of ALH 84001 is partially coated with black fusion crust. The interior is a uniform greenish gray. Photo c/o NASA Johnson Space Center.
PPT Slide
Mars has unusual isotopic abundances: It is rich in
heavy hydrogen, and relatively rich in other
radioactive daughter products.
PPT Slide
Shock Age: The age of the first shock event that heated and crushed the meteor.
Shock age is determined by the ratio of radioactive Potassium to Argon.
40Ar is a gas and comes from decay of radioactive 40K. Argon as a gas escapes from hot rocks but remains trapped in cold rocks.
The measured K-Ar puts the age of ALH 84001 as 4.0 B yrs.
PPT Slide
Argon dating: Argon is a gas. The isotope 40Ar
comes mostly from the decay of the radioactive
isotope of potassium, 40K. Ar escapes from hot
rocks but not from cold ones. So K-Ar ages
represent the last time the rock cooled down.
PPT Slide
Suggestion: Globules contain traces of ancient
Tests show carbonate globules formed 1.39
The cosmic ray exposure analysis tell how
long a meteorite has traveled in space.
Cosmic rays are high energy elementary
When they hit a meteorite they form some
characteristic new isotopes. Isotopes of He,
Ne, and 38Ar can be used. ALH 84001 has
been shown to be in space for ~16 M yrs.
PPT Slide
The possible evidence of life in ALH 84001 was all found in and around carbonate mineral globules. In this microscope view (~0.2 mm across), the cores of the globules are orange-brown, fading outward to colorless, and are surrounded by black and clear bands. The orange-brown mineral in the cores is magnesium-iron carbonate, which grades outward to clear magnesium carbonate. The black bands contain microscopic crystals of iron oxide and sulfide. Other minerals in ALH 84001, which surround the globules, include orthopyroxene and plagioclase. Both are colorless in this view. Photo & copyright Allan Treiman, Lunar and Planetary Institute.
PPT Slide
How long has ALH 84001 been on Earth?
The decay of elements formed by cosmic
ray bombardment give a clue as to the
length of time the meteorite was on Earth.
Carbon 14 dating dating gives a value of
PPT Slide
Is there evidence of fossil life in ALH 84001?
While on Mars it was infiltrated by
The carbonate mineral globules were
They were probably deposited by liquid
The Evidence for Ancient Life in ALH 84001!
The elliptical, rope-like and tubular structures
in the globules are possibly fossil bacteria.
Structure are very small: 20 - 100 billionths
of a meter across. Need an electron microscope
PPT Slide
PPT Slide
Arrows point to the elliptical shapes claimed
to be Martian fossilized bacteria. These
structures are 20 to 100 billionths of a meter
across. They are seen only with an
advanced electron microscope. Are they
actually fossilized bacteria?
Arguments exist on both sides.
PPT Slide
PPT Slide
The mineral grains are similar in shape, size, and
structure to some grains produces by Earth
bacteria. Similar grains can be made by
nonbiological processes as well. Also the grain
in 5c is from a bacterium in a plant root on Earth.
This could not happen on Mars.
PPT Slide
The shapes, although they look like bacteria, are
may not actually be from bacteria.
To show the shapes could really be bacteria, the
1. Be the shape and size of known living
2. Be actually part of the rock - not a
3. Be shown not to be Earth bacteria that
A. Many Earth bacteria have essentially the sane
size and shape of the structures. Further,
“nanobacteria” have been found in Earth rocks
in many different places.
* The structures could also be caused by
inorganic processes, further ancient
Earth bacteria were many times larger.
Need evidence of cell walls.
PPT Slide
B. It has been shown that the structures were not
composed of certain contaminants.
* This is still not proof and there may be
other contaminants responsible.
C. If the structures were from Earth, all meteorites
in the area would have them. It was found that
other non-Martian meteorites from Antarctica
did not have the structures.
*The other meteors were different in
composition. Perhaps Earth bacteria
could only survive in the ALH 84001
but not in the other ones.
PPT Slide
2. Microscopic mineral grains.
Look similar to those from
* Can be made from non biological
processes. See slides 12 and 13.
3. Organic molecules found near the
globules. Could come from the
decomposition of bacteria. They definitely
* The organic molecules found are
not complex enough as those
formed during decomposition of
living organisms. There are other
sources of these molecules.
The organic molecules are significant but do
not prove the existence of life on Mars. There
existence may show pre-biotic activity.