http://www.bbc.co.uk/news/science-environment-16068809

There are some good debate chunks in this.

On Friday, top scientists are meeting at the Geological Society in London to debate this very issue, posing the question: "Is the Earth special?". What emerges is that aspects of our planet and its evolution are remarkably strange.

....Dr Nick Lane, a geneticist at University College London. He believes that the emergence of life is probable on any wet, rocky planet.

...wherever olivine and water mix in large quantities, conditions are favourable for the emergence of life.

Prof Simon Conway Morris, a renowned palaeontologist at the University of Cambridge...."there is a horrible gulf between elementary chemical systems and the creation of fully functioning cells. It is a gap that we have been remarkably unable to bridge experimentally.

I find this type of information/query always interesting.

A very interesting topic of dedate. There was an article in New Scientist a few months back on this. They pointed out that our planet is unusual when compared to planets discovered around other stars. At the time, the sample number was something over 200.

Unusual was the almost circular orbits of old Sol's planets, and the fact that our planetary giants are further out in the solar system. In most of the planets discovered orbiting other stars, the orbits are strongly elliptical, and very large planets orbiting close to the parent star is very, very common. The very large percentage of double and triple star systems may be worth noting also.

These facts are highly significant in terms of life. Circular orbits mean stable climates, and having no giants close to the star means less chance of being tossed out of a stable orbit by the gravity of the giant planet.

Add to that the other factors such as big moon, tectonic action, magnetic field, and being in the 'goldilock's zone' and we can make a solid case for Earth being unusual.

Then, I could mention the Fermi Paradox (http://en.wikipedia.org/wiki/Fermi_paradox) which has many possible explanations. However, the simplest of those explanations is that life, and especially intelligent life is rare in our galaxy. If so, that may be because of the special nature of planet Earth. Quite simply that there are very few equivalants compared to the total number of star systems.

Lance wrote:A very interesting topic of dedate. There was an article in New Scientist a few months back on this. They pointed out that our planet is unusual when compared to planets discovered around other stars. At the time, the sample number was something over 200.

A very, very, very tiny sample.

Lance wrote:
Unusual was the almost circular orbits of old Sol's planets, and the fact that our planetary giants are further out in the solar system. In most of the planets discovered orbiting other stars, the orbits are strongly elliptical, and very large planets orbiting close to the parent star is very, very common. The very large percentage of double and triple star systems may be worth noting also.

Very large planets in orbits close to their star, or in strongly elliptical orbits, are much easier to detect than an earth sized planet. This might make it seem like they are more common than they are. Also, the Kepler mission is surveying a tiny cone of stars in an arm of our galaxy. Can we say this cone is a good representation of the entire galaxy for sure?

Lance wrote:These facts are highly significant in terms of life. Circular orbits mean stable climates, and having no giants close to the star means less chance of being tossed out of a stable orbit by the gravity of the giant planet.

Add to that the other factors such as big moon, tectonic action, magnetic field, and being in the 'goldilock's zone' and we can make a solid case for Earth being unusual.

Sure, the earth is unusual. All these things are necessary for life on Earth. We simply don't know enough to say they are necessary for all life everywhere.

Lance wrote:
Then, I could mention the Fermi Paradox (http://en.wikipedia.org/wiki/Fermi_paradox) which has many possible explanations. However, the simplest of those explanations is that life, and especially intelligent life is rare in our galaxy. If so, that may be because of the special nature of planet Earth. Quite simply that there are very few equivalants compared to the total number of star systems.

That may be true. However, I have the feeling we just don't know enough about the universe to determine what the simplest explanation is.

In their ways, Venus and Uranus (and Neptune, on account of Triton) are unusual, too. While I'm aware that there are many more ways of unusualness than those that favour the evolution of life, this is a hint that oddballs of any kind may not be too rare among planets.