Lecture 15
The Mars Meteorite
(chapter 8.5--Bennett)

The discovery of the unique martian meteorite

4.5 b.y.a.---------------Crystallized from molten rock
4.0 b.y.a----------------Shocked by an impact, but not ejected from surface
1.8-3.6(?) b.y.a------- Carbonate minerals depositied by water flowing through the rock
16 m.y.a.---------------Ejected to space by an asteroid impact
13,000 y.a.----------------Landed on Earth
1984--------------------Collected in Antarctica and classified as a diogenite meteorite
1994--------------------Reclassified as a martian meteorite

from Jakosky, 1998, pg. 145

Events in the history of the martian meteorite ALH84001.  The occurence of each of the geological events is indicated by geochemical evidence, and the dates are determined using various isotopic indicators.

Here is a video showing the infered history of ALH84001.

Evidence for fossilized life in ALH84001


Click here for more images of ALH84001, including an image of the orange carbonate globules.

To show that shapes could really be fossil bacteria, McKay and co-workers have tried to show that:

Microscopic mineral grains are present in ALH84001 like some produced by living and fossil bacteria on Earth.  McKay and co-workers suggest that these mineral grains in ALH84001 may have been produced by martian bacteria by arguing that:

Organic chemical compounds, or polycyclic aromatic hydrocarbons (PAHs), that resemble the decay products of bacteria on Earth found in ALH84001.

McKay and co-workers argue that PAHs in ALH84001 are derived from ancient martian bacteria by trying to show that they are not contamination from laboratory procedures. Further, they contend:

However, scientists later found terrestrial bacteria living inside the meteorite! At least some contamination took place.

Still, it doesn't prove (nor disprove) that there was past life on Mars.

Traces of amino acids found in this and other meteorites support the idea that building blocks of life are common in Universe.

This leads to an interesting corollary -- panspermia.

Did life on Earth come from Mars or a comet or a Leonid meteor shower?

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