Parts of the rock show signs of having been melted and reformed a second time since its birth, which would have been tough to explain if the rock were all original Martian crust.“That had been a bit of a problem,” Treiman says.
Because the isotope composition of this sample plotted on the meteorite isochron, it suggested that earth had the same age and origin as meteorites, therefore solving the age of the Earth and giving rise to the name 'geochron'. Animation shows progressive growth over 4550 million years (Myr) of the lead isotope ratios for two stony meteorites (Nuevo Laredo and Forest City) from initial lead isotope ratios matching those of the Canyon Diablo iron meteorite.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.Lead–lead dating is a method for dating geological samples, normally based on 'whole-rock' samples of material such as granite.For most dating requirements it has been superseded by uranium–lead dating (U–Pb dating), but in certain specialized situations (such as dating meteorites and the age of the Earth) it is more important than U–Pb dating. As evident by the equation, initial Pb isotope ratios, as well as the age of the system are the two factors which determine the present day Pb isotope compositions.As illustrated in figure 1, this point defines the lower (left) end of the isochron.
Therefore, troilite found in Canyon Diablo represents the primeval lead isotope composition of the solar system, dating back to 4.55 /- 0.07 Byr.
By comparing the amount of the parent element to the daughter element, scientists can infer how long a rock has been around.“To understand how the Martian mantle has evolved, it’s critical to get samples that are old, to see what the mantle sources were early in the planet’s history,” says Thomas Lapen of the University of Houston, a coauthor of the new study.
“This is the only sample in that age range.”Lapen and his colleagues used radioactive isotope dating to calculate the age of the meteorite, using different elements than the 1995 analysis did.
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.