Oldest rocks meteors
Fragments of the Tagish Lake meteorite landed upon the Earth on January 18, 2000 at 16:43 UT (08:43 local time in Yukon) after a large meteoroid exploded in the upper atmosphere at altitudes between 50 and 30 km with an estimated total energy release of about 1.7 kilotons. Following the reported sighting of a fireball in the in southern Yukon and northern British Columbia, Canada,
Based on eyewitness accounts of the fireball caused by the incoming meteorite and on the calibrated photographs of the track which it had left behind and which was visible for about half an hour, scientists have managed to calculate the orbit it followed before it impacted with Earth. Although none of the photographs captured the fireball directly, the fireball path was reconstructed from two calibrated photos taken minutes after the event, giving the entry angle. Eyewitness accounts in the vicinity of Whitehorse, Yukon accurately constrained the ground track azimuth from either side. It was found that the Tagish Lake meteorite had a pre-entry Apollo type orbit that brought it from the outer reaches of the asteroid belt. Currently, there are only eleven meteorite falls with accurately determined pre-entry orbits, based on photographs or video recordings of the fireballs themselves taken from two or more different angles.
Further study of the reflectance spectrum of the meteorite indicate that it most likely originated from 773 Irmintraud, a D-type asteroid.
Angrites are one of the rarest of the meteorite classes with only 8 specimens
known. They are basaltic in origin and are the oldest of all basaltic
achondrites (4.57 billion years). Their textures, like that shown for the
angrite D' Orbigny, the presence of vesicles in some examples, and elemental
distributions suggest that the angrites crystallized rapidly, either within a
meter of the surface or as surface flows.
But then I have read that D'Orbigny, stated by Qing-Zhu Yin (2009) is the
oldest meteorite, with an age of 4,567.91 (+- 0.76) m.y. But to counter
Qing-Zhu Yin claim, in 2009 Tistarite a new refractory mineral was found in
Allende which this new refractory mineral is among the first solids formed in
the solar system ( American Mineralogist 2009 ).
The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 1:05 a.m. on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and it is often described as "the best-studied meteorite in history". The Allende meteorite is notable for possessing abundant, large calcium-aluminium-rich inclusions, which are among the oldest objects formed in the Solar System.
The original stone is believed to have been approximately the size of an automobile traveling towards the Earth at more than 10 miles per second. The fall occurred in the early morning hours of February 8, 1969. At 1:05 a.m., a huge, brilliant fireball approached from the southwest and lit the sky and ground for hundreds of miles. It exploded and broke up to produce thousands of fusion crusted individuals. This is typical of falls of large stones through the atmosphere and is due to the sudden braking effect of air resistance. The fall took place in northern Mexico, near the village of Pueblito de Allende in the state of Chihuahua.
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
The discovery at California Institute of Technology in 1977 of new forms of the elements calcium, barium and neodymium in the meteorite was 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 - the explosion of an aging star - 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
But some people have a different idea of the
age old question and feel that the
Vigarano meteorite is the oldest meteorite. Vigarano fell at 9:30 pm 22 January
1910 in Emilia, Italy. Two stones of 11.5 kg and 4.5 kg were found. This is
the type specimen for the CV class. A case can be made for Vigarano being
the oldest meteorite.