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# Life on Earth Celebration
A water-balloon fight to celebrate the anniversary of the first life on Earth.
## The first life on Earth
### The Cosmic Calendar
The Cosmic Calendar is made by pretending that the universe is exactly one year
old.
The universe was born on January 1st, at midnight, the beginning of this year;
and it will reach its present age on midnight, December 31st, at the end of this
year.
Since the universe is actually 14 billion years old:
* One month on the Cosmic Calendar is 1.1 billion years.
* One day on the Cosmic Calendar is 38 million years.
and
* One second on the Cosmic Calendar is 437 years.
#### Today, on October 1st, the universe becomes 10 months old.
That means today we commemorate the time when the universe was 10.3 billion
years old. Or, about three and a half billion years ago. That was a very special
time, because it was then that life first formed on Earth.
In fact, life probably began around September 23rd -- 3.8 billion years ago. We
chose this day to celebrate because of the weekend and the nice weather.
But the earliest fossils which prove to a certainty that life existed date from
exactly tomorrow -- October 2nd -- 3.4 billion years ago. So today's date works
out pretty well either way.
## Why water balloons?
When Rory was four years old, Ella left her alone with me one night to go to a
Mom's night out. We were looking at photographs of the desert and at some point
I told her that humans are mostly made out of water -- and she did _not_ believe
me! How can humans be made of water? Why doesn't the water spill out? I went to
the kitchen and filled up six zip lock bags with water and stacked them up on
the table. Humans are made up of little _bags_ of water called cells. All life
is made up of cells, except for viruses which can only live inside the cells of
other life forms. This is why the water balloon is a symbol of all life.
The water balloon is also fun to play with. It is fun because it is unstable --
it is easily broken -- and when that happens, the water _does_ all spill out!
Today we are going to get wet, or at least those of us who are kids are going to
get wet. And then we will dry off and warm up by the fire.
It's a bit late in the year for water balloon fights but it's a nice day today,
just nice enough. It's may be the last day of the year when we can get wet and
still have fun. Soon it will be cold.
This is also fitting the theme of the first life on Earth, because on the cosmic
calendar, life is a phenomenon of fall and the winter.
In the history of the Earth, life is also connected closely with cooling down.
Just three weeks ago, on September 6th -- Rory's Birthday -- the planet Theia
collided with Earth, forming the Moon. The Moon was not formed from the mass of
Theia, though; Theia and Earth were thoroughly mixed together. The two planets
became one exploding mass, and the remnants of the explosion became the Moon.
Those remnants were so hot that they were made out of vaporized rock. Not liquid
lava, but liquid lava turned into vapor. _Thankfully_, things have cooled down
since then. In just about 100 years of real time, the doughnut-shaped cloud of
rock vapor cooled down enough to become the Moon. And in a short 600 million
years, or 17 cosmic days, the Earth itself cooled down enough to allow for life
to begin.
So as the days get cooler and become cold, or if you happen to get cold and wet
today, remember to be thankful.
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