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Founded January 1970
Julian Date: 2458864.16
2019-2020:  LXXXV
               "Portland's Space Place."

THE DAILY ASTRONOMER
Wednesday, January 15, 2020
The Oldest Stuff on Earth

Want to contemplate a notion that will make you feel as though you're
living precariously atop a particularly thin cloud?   There was a time,
billions of years in fact, when Earth didn't exist.   The material that
would ultimately comprise Earth did exist, of course, albeit in a different
form and in widely scattered places throughout the galaxy.      According
to the heretics, the solar system coalesced out of a nebula approximately
4.5 - 5 billion years ago.  Earth is about 4.5 billion years old. The Sun
is slightly older. Our Universe began about 13.8 billion years ago.   If we
do a little arithmetic, we can determine that the cosmos got along
swimmingly without our precious Terra Firma for the better part of nine
billion years!

This paragraph brings us neatly -we hope- to today's brilliant question:

*"In today’s news:  scientists have discovered dust that is 7 billion years
old.  Long before planet earth even existed!  How can that be?
And....aren’t we continually being bombarded by cosmic dust that is
billions and billions of years old? So what’s the big deal? "   -S.H.*

Greetings!
First, let's trip back to 1969, a particularly monumental year for
astronomy.  On September 28, 1969 around 10:58 a.m., residents in and
around Murchison, in the Australian state of Victoria, marveled at the
sight of a brilliant fireball separating into three fragments high in the
sky: an asteroid in fiery descent.    Soon thereafter the observers felt a
powerful tremor as fragments of the interplanetary inteloper crashed onto
the ground.     The remnants of what would ultimately become known as the
Murchison Meteorite were scattered over more than five square miles!
 While most fragments were small, the cumulative mass of all the collected
pieces equalled about 220 kilograms (110 lbs): a veritable treasure trove
for planetary scientists.

The Murchison Meteorite is a carbonaceous chondrite, meaning that it's
carbon rich and contains some of the most primitive material in the solar
system.      So primitive, in fact, that this month astronomers announced
that silicon carbide particles extracted from one of the meteorite
fragments is approximately seven billion years old:  far older than planet
Earth. These little meteoritic particles are now known to be the oldest
stuff on Earth.

But, wait, how is that possible?
To answer this question, we have to rewind back billions of years in the
past to the time when a Type II supernova (a star that exploded from the
inside out at its life's end) scattered its material radially through its
local interstellar environment.  Some of this material mixed with a cold,
hydrogen laden nebula and precipitated a collapse.   After a few million
years, the collapsing cloud formed the Sun and its retinue of attendant
planets and other bodies, including the myriad asteroids, more than a
billion of which still remain in our solar system.    Therein lies the
secret.    The asteroids have generally experienced no geological activity
since their formation.     They have been frozen in time, which makes them
so coveted by planetary scientists who want to study the solar system's
infancy.       As all the material comprising Earth has undergone melting,
vaporization, massive upheavals and other transformations throughout the
planet's long life, it doesn't remain in the same form chemically as it was
during the early days of the solar system.

The silicon carbides imbedded within the Murchison meteorite were formed
about seven billion years ago!  They became incorporated into the
now-famous asteroid that crashed on Earth in 1969.     As their formation
predates Earth's development by about 2.5 billion years, researchers know
that these particles are the oldest known material on Earth!

Yes, we are constantly bombarded by dust that is billions of years old.  It
is highly likely that some of this material might also predate Earth's
formation, considering that meteorites are fragments of asteroids and
comets, both of which originate in the early solar system.  The problem is
the identification.  Even most micro meteorites undergo significant heating
during their descent through the atmosphere and as a consequence experience
chemical and physical changes.

We should point out that all the atoms comprising our world (and us)
pre-date Earth's formation.   We are all formed of ancient material dating
back to the early Universe.   This statement applies to everything,
incidentally: from the asphalt in front of your local supermarket, to the
snow squalls gathered around Everest's summit to the tips of your eyelids.
   The problem is that in all the aforementioned, the atoms were shifted
from one molecule to another, often multiple times.     The material in the
meteorite has remained chemically the same for the past seven billion years.

It is the oldest stuff on Earth whose age has been determined: lending
evidence to support the frightening notion that so much material existed
 overly immensely long time scales prior to the formation of our home
planet.




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