http://www.psrd.hawaii.edu/May10/YoungerALH84001.html

Younger Age for Oldest Martian MeteoriteYounger Age for Oldest Martian MeteoriteLong Geologic History

Formation by crystal accumulation in a magma chamber

Shocked and crushed by impact

Aqueous alteration and deposition of carbonate globules

Isotopic systems, hence ages, affected by shock and alteration

http://www.psrd.hawaii.edu/May10/YoungerALH84001.html

Younger Age for Oldest Martian MeteoriteYounger Age for Oldest Martian Meteorite

Igneous formation age of ALH84001 is 4.09 Ga, much younger than the previously-reported Sm-Nd age of 4.50 Ga.

http://www.psrd.hawaii.edu/May10/YoungerALH84001.html

Younger Age for Oldest Martian MeteoriteYounger Age for Oldest Martian Meteorite

Next step: Reconcile igneous, impact, and alteration events recorded in ALH84001 with ages of impact basins on Mars.

Frey (2010)