Martian Meteorites and Fossil Martians

1996: Team of NASA scientists made the following claim:

A meteorite which came from Mars has signs of fossilized bacterial life.

Wow. Alan Hills 840001

This meteorite had chondrules, deposits which form when the environment a rock lives in changes. The scientists said these chondrules formed when water seeped through the rock in its early history on Mars.

Around these chondrules, they found evidence for

organic material (materials known as PAHs - polycyclic aromatic hydrocarbons),
signs of magnetite (often associated with Earth bacteria and their interaction with the Earth's magnetic field), and most amazingly,
features which looked like fossilized worms:

If someone came up to you and said that, what questions would you want answered before you believed them?

Is the rock really from Mars?

Yes. Absolutely.

It is chemically similar to a handful of odd meteorites which are not like the vast quantities of normal meteorites we find.
These meteorites are igneous rock -- signs of volcanic activity.
These rocks have trapped gases which are identical to the atmosphere Viking found on Mars.

Age dating of the rock suggests

it was originally formed 4.6 billion years ago.
the carbonate inclusions date from 3.6-4.0 billion years.
16 million years ago, the rock was ejected from Mars in an impact
13,000 it landed in Antarctica
14 years ago it was found.

Could the evidence seen in ALH840001 be produced by chemical processes?

Yes. Absolutely.

PAHs run around throughout space. In comets, dust clouds, etc. Very common.
Magnetite is a common mineral; analysis of the structure of magnetite found in ALH840001 suggests it is inorganic.
The "worms" could easily be mineral-like platelets in the meteorite viewed edge on.

Why is it hard to envision the evidence in ALH840001 as biological?

Carbonate deposits can easily form in shock heated rock at 700K -- not conducive to life.
The structures are 10-20 times smaller than similar "micro fossils" seen on the earth. The smaller objects are probably too small to support DNA: microfossils 20nm; cell walls each 5nm -- not enough room left over for DNA!
Magnetite in Earth bacteria is due to interactions with the Earth's magnetic field -- Mars has no magnetic field. Why would the Mars bacteria excrete magnetite?

Final thoughts

Timing: NASA push for missions to Mars
Scientific community: vast majority of astronomers do not believe the claims are valid.
Carl Sagan: Extraordinary claims require extraordinary evidence