These four ancient rocks were all found
on Earth...but only one of them actually originated here.
The others are pieces of distant worlds. One formed on an
asteroid; another, on the Moon; and the third, on Mars. Impacts
hurled them into space where they drifted for thousandseven
millionsof years before plummeting to Earth as meteorites.
Such precious samples carry evidence of the tumultuous history
of our Solar System.
At 4 billion years old, this gneiss is the oldest known rock
that formed on Earth. The Earth is about 500 million years
older still, but little record of that early time has survived
our planets geologic activity. In this satellite view
of North America, you can see the region of Canada where the
gneiss was found.
We know Shergotty came from Mars because it contains gas whose
composition matches that of Mars's atmosphere as measured
by the U.S. Viking spacecraft. An impact trapped the gas in
the rock and flung it into space. With its giant volcanoes
Marss Tharsis Plateau is the most likely source of the
"young," 180-million-year-old Shergotty meteorite. Few craters
mar the regions lava-covered plains, suggesting that
they are geologically young.
MacAlpine Hills 88105
A meteoroid impact ejected this rock from the Moon 300,000
years ago. It is similar to rocks collected in the lunar highlands
by Apollo astronauts. The light-colored, densely cratered
regions you see in this image of the Moon are lunar highlands.
Such terrain is probably the source of this meteorite.
Cameras operated by the Smithsonian Astrophysical Observatory
recorded Lost City's fall in 1970. The photos enabled scientists
to reconstruct the meteorite's orbit and determine that it
originated in the asteroid belt. We don't know which asteroid
the Lost City meteorite came from, but it may have looked
similar to the asteroid Ida.