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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.
+