- 4243 - MOON - how old is the moon? An object the size of Mars crashed into the Earth over 4 billion years ago, creating a cloud of debris that formed the Moon. When the Apollo astronauts landed on the lunar surface, they found and brought back Moon rocks that helped pinpoint when this event happened.
------------------------- 4243 - MOON - how old is the moon?
- See Review 4242
for discoveries of the oldest galaxies.
This Review is about the age of the Moon. And, the
Moon is 40 million years older than we thought.
-
- A new study of
crystals in the lunar samples pushed that event back even further , about
40,000,000 years earlier than previous estimates, setting the Moon’s formation
to about 4.46 billion years old. This is
not long after the Earth formed.
-
- Scientists used an
“atom-probe tomography” facility to study Moon rocks and dust collected during
the Apollo 17 mission in 1972. This facility allowed them to perform an
improved form of radiometric dating.
-
- Radiometric dating
calculates an age in years for geologic materials by measuring the presence of
a short-life radioactive element, such as carbon-14, or a long-life radioactive
element plus its decay time.
-
- The facility,
which includes a sensitive high-resolution ion microprobe, allowed the
researchers to look at every atom in the zircon crystals and count how many of
the atoms have undergone radioactive decay. When an atom undergoes decay, it
sheds protons and neutrons to transform into different elements.
-
- Uranium decays
into lead, and zircon contains the radioactive element uranium. Uranium has
been called “the clock within zircon” because it converts to the element lead
at a specific rate over a long span of time.
-
- This study is a
testament to immense technological progress we have made since 1972 when the
last crewed Moon mission returned to Earth.
These samples were brought to Earth half-a-century ago, but only today
do we have the necessary tools to perform microanalysis at the requisite level,
including “atom-probe tomography.”
-
- When the Mars-size
object hit the Earth and formed the Moon, the energy of the impact melted the
rock that eventually became the Moon’s surface.
When the surface was molten like that, zircon crystals couldn’t form and
survive. So, any crystals on the Moon’s
surface must have formed after this lunar magma ocean cooled. Otherwise, they
would have been melted and their chemical signatures would be erased.
-
- Apollo 17 was the
sixth and final Apollo mission to land people on the Moon and was the only
Apollo mission to have a trained geologist among its crew. Lunar module pilot
and geologist Harrison Schmitt joined Commander Gene Cernan and Command Module
Pilot Ron Evans. The astronauts landed on the southeastern rim of the
Serenitatis Basin, known as Taurus-Littrow. Schmitt and Cernan collected about
243 pounds of soil and rock samples that were brought back to Earth for further
study. Previous studies concluded that the samples from Apollo 17 came from the
oldest known impact craters on the Moon.
-
- For the new
experiment on these samples, a small portion of the lunar sample was sharpened
into a very sharp tip, using a focused ion beam microscope. UV lasers evaporate atoms from the surface of
that tip. The atoms travel through a mass spectrometer, and how fast they move
provides evidence of how heavy they are, which in turn tells the scientists
what the atoms are made of.
-
- These crystals are
the oldest known solids that formed after the giant impact. Because we know how old these crystals are,
they serve as an anchor for the lunar chronology.
-
- Radiometric dating
works somewhat like an hourglass. In an
hourglass, sand flows from one glass bulb to another, with the passage of time
indicated by the accumulation of sand in the lower bulb. Radiometric dating works similarly by
counting the number of parent atoms and the number of daughter atoms they have
transformed to. The passage of time can then be calculated because the transformation
rate is known.
-
- A previous study
suggested this older age of the lunar surface.
They used the atom probe tomography facility at Northwestern to get a
nano-scale look at the lunar samples, which confirmed the age of this oldest
known lunar crystal
-
- This is an anchor
point for so many questions about the Earth. When you know how old something
is, you can better understand what has happened to it in its history. It stabilizes the Earth’s rotational axis,
it’s the reason there are 24 hours in a day, it’s the reason we have tides.
-
- Without the Moon,
life on Earth would look different. It’s a part of our natural system that we
want to better understand, and this study provides a tiny puzzle piece in that
whole picture. Maybe we can find out how
old Duane is. Get a sample from his
coffee cup.
-
-
November 27, 2023
MOON - how old is the moon? 4242
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Tuesday, November 28, 2023 ---------------------------------
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