Welcome. And congratulations. I am delighted that you could make it. Getting here wasn't
easy, I know. In fact, I suspect it was a little tougher than you realize.

To
begin with, for you to be here now trillions of drifting atoms had
somehow to assemble in an intricate and intriguingly obliging manner to
create you. It's an arrangement so specialized and particular that it
has never been tried before and will only exist this once. For the next
many years (we hope) these tiny particles will uncomplainingly engage
in all the billions of deft, cooperative efforts necessary to keep you
intact and let you experience the supremely agreeable but generally
underappreciated state known as existence.
Why atoms take this
trouble is a bit of a puzzle. Being you is not a gratifying experience
at the atomic level. For all their devoted attention, your atoms don't
actually care about you-indeed, don't even know that you are there.
They don't even know that they are there. They are mindless particles,
after all, and not even themselves alive. (It is a slightly arresting
notion that if you were to pick yourself apart with tweezers, one
atom at a time, you would produce a mound of fine atomic dust, none of
which had ever been alive but all of which had once been you.) Yet
somehow for the period of your existence they will answer to a single
overarching impulse: to keep you you.

The bad news is that atoms
are fickle and their time of devotion is fleeting-fleeting indeed. Even
a long human life adds up to only about 650,000 hours. And when that
modest milestone flashes past, or at some other point thereabouts, for
reasons unknown your atoms will shut you down, silently disassemble,
and go off to be other things. And that's it for you.

Still, you may
rejoice that it happens at all. Generally speaking in the universe it
doesn't, so far as we can tell. This is decidedly odd because the atoms
that so liberally and congenially flock together to form living things
on Earth are exactly the same atoms that decline to do it elsewhere.
Whatever else it may be, at the level of chemistry life is curiously
mundane: carbon, hydrogen, oxygen, and nitrogen, a little calcium, a
dash of sulfur, a light dusting of other very ordinary elements-nothing
you wouldn't find in any ordinary drugstore-and that's all you need.
The only thing special about the atoms that make you is that they make
you. That is of course the miracle of life.

Whether or not atoms
make life in other corners of the universe, they make plenty else;
indeed, they make everything else. Without them there would be no water
or air or rocks, no stars and planets, no distant gassy clouds
or swirling nebulae or any of the other things that make the universe
so usefully material. Atoms are so numerous and necessary that we easily overlook
that they needn't actually exist at all. There is no law that requires
the universe to fill itself with small particles of matter or to
produce light and gravity and the other physical properties on which
our existence hinges. There needn't actually be a universe at all. For
the longest time there wasn't. There were no atoms and no universe for
them to float about in. There was nothing-nothing at all anywhere.

So
thank goodness for atoms. But the fact that you have atoms and that
they assemble in such a willing manner is only part of what got you
here. To be here now, alive in the twenty- first century and smart
enough to know it, you also had to be the beneficiary of an
extraordinary string of biological good fortune. Survival on Earth is a
surprisingly tricky business. Of the billions and billions of species
of living thing that have existed since the dawn of time, most-99.99
percent-are no longer around. Life on Earth, you see, is not only brief
but dismayingly tenuous. It is a curious feature of our existence that
we come from a planet that is very good at promoting life but even
better at extinguishing it.

The average species on Earth lasts
for only about four million years, so if you wish to be around for
billions of years, you must be as fickle as the atoms that made you.
You must be prepared to change everything about yourself-shape, size,
color, species affiliation, everything-and to do so repeatedly. That's
much easier said than done, because the process of change is random. To
get from "protoplasmal primordial atomic globule" (as the Gilbert and
Sullivan song put it) to sentient upright modern human has required you
to mutate new traits over and over in a precisely timely manner for an
exceedingly long while. So at various periods over the last 3.8 billion
years you have abhorred oxygen and then doted on it, grown fins and
limbs and jaunty sails, laid eggs, flicked the air with a forked
tongue, been sleek, been furry, lived underground, lived in trees, been
as big as a deer and as small as a mouse, and a million things more.
The tiniest deviation from any of these evolutionary shifts, and you
might now be licking algae from cave walls or lolling walrus-like on
some stony shore or disgorging air through a blowhole in the top of
your head before diving sixty feet for a mouthful of delicious
sandworms.

Not only have you been lucky enough to be attached
since time immemorial to a favored evolutionary line, but you have also
been extremely-make that miraculously-fortunate in your personal
ancestry. Consider the fact that for 3.8 billion years, a period of
time older than the Earth's mountains and rivers and oceans, every one
of your forebears on both sides has been attractive enough to find a
mate, healthy enough to reproduce, and sufficiently blessed by fate and
circumstances to live long enough to do so. Not one of your pertinent
ancestors was squashed, devoured, drowned, starved, stranded, stuck
fast, untimely wounded, or otherwise deflected from its life's quest of
delivering a tiny charge of genetic material to the right partner at
the right moment in order to perpetuate the only possible sequence of
hereditary combinations that could result-eventually, astoundingly, and
all too briefly-in you.

Extracted from the book - A short history of nearly everything. It's long but is worth it.