Earth - Our Island Home


Little Earth, the only home we have ever known

This is the famous picture shot from the Moon in 1968.
It stunned everybody with its lesson.

Click for full size 2400 x 2400 view in a new window.


The Earth has many characteristics that support life:

Goldilocks Zone: Earth has an almost circular orbit in what astronomers call a Goldilocks zone in its solar system, where the temperature supports liquid water and is fairly stable. We have now found about 4 thousand planets around nearby stars, a few in Goldilock zones.

Good Neighborhood: It is in a safe location in its galaxy, away from the turbulent center of the galaxy in a stable solar system. But it is also in a galactic region with many materials that support the chemical processes of life. All this makes a sort of galactic Goldilocks zone too.

Our nearest neighbor - the Moon

Good Neighbors: Earth has a large moon that stirs the planet’s materials like the ocean and surface tectonic plates of the continents, but not too much - like a soup pot on simmer. It is an inner "rocky" planet in its solar system, somewhat protected by gas giant outer planets that soak up lots of the debris still falling in from our solar system's formation.

Nice Construction: Earth has lots of water. In fact our planet's surface is over two thirds water and probably ought to be called Oceania instead of Earth. Water provided the medium for the development of life. Earth has an iron core, providing a strong magnetic field that helps to protect it from radiation and the solar wind. Earth is also big enough to have enough gravity to hold on to its atmosphere - unlike Mars. The makeup of the atmosphere has changed over time, fortunately for us, since we breathe oxygen - a later product of life proceses here.

Luck: Earth has taken a few hard hits, but not too many or too big. Life has almost been wiped out here several times, but recovered. Sometimes these catastrophes lead to fortunate changes like clearing the dinosaurs away enough to make room for mammals - us.

Life: LIfe is so strong here that it has actually modified the planet, changing the ocean, covering the surface and charging the atmosphere with oxygen - the waste products of chlorophyll plants and some microbes. The development of life has several stages: the gathering or development of materials, the development of microbes.

Intelligent Life: While the development of microbes may be fairly common throughout the universe, the long term survival of a planet's life for the development of intelligence may be rare. See  Rare Earth, by Peter Ward & Donald Brownlee

Frank Drake's Equation: At the Green Bank, WV Radio Astronomy Observatory  there is a plaque on the wall  in a meeting room with an equation Frank Drake cooked up for discussion. Frank attempted to calculate the frequency of life in this galaxy by multiplying the number of stars in our galaxy by some other factors.  For more see this Wikipedia article. 


Meanwhile: Many people calculate that there are thousands of civilizations in our galaxy - the Milky Way. BUT when I use my best estimates with Frank's equation, I come up with only a few - maybe only one, OR even ZERO, per galaxy. See: 

Is this because of the Great Filter? Here is another good article about the Fermi Paradox = where are they?  Why don’t we see others besides us here?

Try your hand at calculating the probability of life like ours using Frank's equation with this link. 

Arthur C Clarke:
"There are two possibilities - we are alone in the universe or we are not.
In either case, the thought is staggering”



“I don’t think we were thrown out of the Garden of Eden. 
Just look around. We’re still in it ...” 
— Alan Bean,  Apollo 12


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© Gareth Harris 2019                                      Email:                  See also: