[ETL]

The Mars rock is believe to have landed on Earth only about 13,000 years ago. The potential fossilized micros within it are billions of years old.

From NASA.gov:

1. The original igneous rock solidified within Mars about 4.5 billion years ago, about 100 million years after the formation of the planet. (Based on isotope ages of the igneous component of the meteorite)

2. Between 3.6 and 4 billion years ago the rock was fractured, presumably by meteorite impacts. Water then permeated the cracks, depositing carbonate minerals and allowing primitive bacteria to live in the fractures.

3. About 3.6 billion years ago, the bacteria and their by-products became fossilized in the fractures. (Based on isotope ages of the minerals in the fractures)

4. 16 million years ago, a large meteorite struck Mars, dislodging a large chunk of this rock and ejecting it into space. (Based on the cosmic ray exposure age of the meteorite)

5. 13,000 years ago, the meteorite landed in Antarctica.

6. The meteorite, ALH84001, was discovered in 1984 in the Allan Hills region of Antarctica.

http://nssdc.gsfc.nasa.gov/planetary/marslife.html

[aimhigh]

The potential fossilized micros within it are billions of years old.

There's no way to gauge the age of Martian fossil. They must "assume" carbon 12 dating is identical on another planet. That's a big assumption.