Radiogenic dating of meteorites
The oldest known Martian meteorite isn’t so old after all.
Though it’s still the oldest chunk of Mars scientists have ever found, new research suggests the Allan Hills meteorite – officially known as ALH84001 – is about 400 million years younger than previously estimated.
The previously accepted age of 4.51 billion years old was calculated in 1995 by measuring radioactive isotopes of samarium and neodymium.
Radioactive elements decay from a “parent” isotope (in this case, samarium) to a “daughter” isotope (neodymium) at a set rate.
Surprisingly, the researchers also found that several younger meteorites have essentially the same composition as the Allan Hills meteorite, meaning some of the same basic geologic processes have been at work on Mars for almost its entire history.“That connection is perhaps the most amazing outcome of this research,” Lapen says. Igneous processes were happening the same way four billion years ago as they are happening right now.”The new age places the rock’s birth date right at a period in the solar system’s history when all of the inner planets were being bombarded with meteorites.
That could clear up some confusion about the meteorite, Treiman says.
They led to the discovery that certain very heavy elements could decay into lighter elements – such as uranium decaying into lead.The scientific community has since mostly abandoned that idea, as one by one every line of evidence for life has been given a non-biological explanation.“People usually ask me about the life aspect, and I’m so sick to death of that,” says Allan Treiman of the Lunar and Planetary Institute in Houston, who was not involved in the new work.Treiman and others now believe that what once looked like fossils is actually rock that was shaped by ordinary geological activity.“Then ages dependent on the phosphates are altered.”Instead of elements found in phosphates, Lapen’s group used lutetium and hafnium, elements that are mostly found in more change-resistant components of the rock.
This method showed that the meteorite is just 4.091 billion years old.The Allan Hills meteorite, named for the site where it was found in Antarctica, was once thought to contain fossil traces of life.