A number of museums launched expeditions to Mexico to collect samples. The Allende meteorite contains chondrules and CAIs that are estimated to be 4.567 billion years old,
the oldest known matter (other carbonaceous chondrites also contain
these). This material is 30 million years older than the Earth and 287
million years older than the oldest rock known on Earth, Thus, the
Allende meteorite has revealed information about conditions prevailing
during the early formation of our solar system. The CAIs had very unusual isotopic
compositions, with many being distinct from the Earth, Moon and other
meteorites for a wide variety of isotopes. These "isotope anomalies"
contain evidence for processes that occurred in other stars before the
solar system formed. This was a time of great excitement
and energy among planetary scientists. Allende is one of the most primitive meteorites and
contain the most primitive known matter. They have undergone the least
mixing and remelting since the early stages of solar system formation.
Because of this, their age is frequently taken as the "age of the solar
Composition - The matrix and the chondrules consist of many different minerals, dominantly olivine and pyroxene. Allende is classified as a CV3 carbonaceous chondrite: the chemical composition, which is rich in refractory volatile elements like Na and K, places it in the CV group, and the lack of secondary heating effects is consistent with petrologic type 3. Like most carbonaceous chondrites and all CV chondrites, Allende is enriched in the isotope O-16 relative to the less abundant oxygen isotopes, O-17 and O-18. There was found to be a small amount of carbon (including graphite and diamond), and many organic compounds, including amino acids, some not known on Earth. Iron, mostly combined, makes up about 24% of the meteorite.Subsequent research - Close examination of the chondrules in 1971, by a team from Case Western Reserve University, revealed tiny black markings, up to 10 trillion per square centimeter, which were absent from the matrix and interpreted as evidence of radiation damage. Similar structures have turned up in lunar basalts, but not in their terrestrial equivalent which would have been screened from cosmic radiation by the Earth's atmosphere and geomagnetic field. Thus it appears that the irradiation of the chondrules happened after they had solidified but before the cold accretion of matter that took place during the early stages of formation of the solar system, when the parent meteorite came together.
The discovery at California Institute of Technology in 1977 of new forms of the elements calcium, barium and neodymium
in the meteorite is believed to show that those elements came from
some source outside the early clouds of gas and dust that formed the
solar system. This supports the theory that shockwaves from a supernova may have triggered the formation of,
or contributed to the formation of our solar system. As further
evidence, the Caltech group said the meteorite contained Aluminum
26, a rare form of aluminum. This acts as a "clock" on the meteorite,
dating the explosion of the supernova to within less than 2 million
years before the solar system was formed. Subsequent studies have found isotopic ratios of krypton, xenon nitrogen and other elements that are also unknown in our solar system. The
conclusion, from many studies with similar findings, is that there were
a lot of substances in the presolar disc that were introduced as fine
"dust" from nearby stars, including novas, supernovas, and red giants. These specks persist to this day in meteorites like Allende, and are known as presolar grains.