The well-known Martian meteorite, ALH84001 is unique among Mars rocks available for study on Earth, since its formation age is more than 2.5 billion years older than any other recognized Martian meteorite, giving scientists the only sample of material formed early in Mars' history.
The true age of this meteorite is has now been determined to be 4.091 billion years old, about 400 million years younger than earlier age estimates. This stone formed during an important time when Mars was wet and had a magnetic field, conditions that are favorable for the development of simple life. This finding precludes ALH84001 from being a remnant of primordial Martian crust, as well as confirming that volcanic activity was ongoing in Mars over much of its history.
"This research helps us better refine the history of Mars," Lapen said. "This has huge ramifications for our understanding of volcanic processes active in Mars and for the nature of deeper portions of the planet that are sources of magmas that produced the largest volcanoes in the solar system. These data also are used to refine models of initial planetary formation and early evolution." link
From Planet Comics #50 (Sept., 1947)
Art by Murphy Anderson © Fiction House
Ref.: A Younger Age for ALH84001 and Its Geochemical Link to Shergottite Sources in Mars. T. J. Lapen, et al. Science 328: 347 - 351.
Abstract: Martian meteorite ALH84001 (ALH) is the oldest known igneous rock from Mars and has been used to constrain its early history. Lutetium-hafnium (Lu-Hf) isotope data for ALH indicate an igneous age of 4.091 ± 0.030 billion years, nearly coeval with an interval of heavy bombardment and cessation of the martian core dynamo and magnetic field. The calculated Lu/Hf and Sm/Nd (samarium/neodymium) ratios of the ALH parental magma source indicate that it must have undergone extensive igneous processing associated with the crystallization of a deep magma ocean. This same mantle source region also produced the shergottite magmas (dated 150 to 570 million years ago), possibly indicating uniform igneous processes in Mars for nearly 4 billion years.
Syd Barrett & Astronomy Domine