Through the study of a popular Martian meteorite's age, University of Houston researchers have uncovered important details about the history of volcanic activity on Mars.

ALH84001 is a thoroughly studied, well-known Martian meteorite, 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, it offers scientists the only view of Mars' early history. Data from this rock may also help geologists better understand, through analogy, the processes of early Earth evolution.

The new analysis of ALH84001 is published in Science
Researchers showed that the true age of this meteorite is 4.091 billion years old, about 400 million years younger than earlier age estimates. They concluded that 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," said Alan Brandon, an associate professor in UH's department of earth and atmospheric sciences. "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."

With the crystallization age and formation of this rock being debated since its discovery in 1984, Lapen researchers seized an opportunity to better refine the early history of Mars. With samples provided by the NASA Antarctic meteorite curator and the meteorite working group, the researchers used a relatively new method that has never been applied to this stone – lutetium-hafnium isotope analysis.

"We studied variations in isotopic compositions of minerals to determine the age and sources of magmas that produced these rocks," Lapen said. "We uncovered evidence that the volcanic systems in Mars were likely active more than four billion years. This connection allows the possibility that regions with the largest volcanoes in the solar system perhaps host some of the longest-lived volcanic systems in the solar system."

Citation: Lapen et al., 'A Younger Age for ALH84001 and Its Geochemical Link to Shergottite Sources in Mars', Science, April 2010, 328(5976), 347 - 351; doi: 10.1126/science.1185395