Earth is a rocky planet, just like the other first four planets orbiting Sol, Earth's sun. But Earth is definitely unique due to the vast variation of life on Earth. It is possible that some of the nearby neighboring planets, notably Venus and Mars, may have at one time supported some form of life, but it is evident from current observation that only Earth holds the distinction of dynamic life today.
Life on Earth has existed since early life began being formed about three billion years ago. When primitive cells found a way to harness the energy of the sun, such as occurs in photosynthesis, life started slowly, then erupted with great diversity. Scientists at MIT, Massachusetts Institute of Technology, studied mathematical models of life by looking at 1,000 key genes and calculating their past, distant origins through a genome project devised by Eric Alm and Lawrence David.
Earth is unique for other reasons as well. No other known planet has vast oceans of liquid water, a breathable atmosphere or this planet's specific gravity. No other planet has the exact amount of sunlight and chemistry to support life such as Earth's. No other planet in the solar system is balanced with vast interactive systems of air, water, soil, minerals and more.
Life is so unique that for most of human history, the anthropic principle, which assumes all of the creation is specifically designed for the existence of human life, prevailed. It is a recent idea that earth is not the center of the universe. It is an even more recent idea that man is not the pinnacle of creation, and that life itself is not likely to be unique in the vast cosmos.
That this idea has arrived is still controversial to many people. Science and religion seem to be in a tug of war over how life was created and why. The Earth itself has only very recently been realized to be finite and in need of protection from overuse and exploitation.
It is a matter of current critical importance that people begin to use their highly evolved brains to realize how rare and precious life on Earth actually is. Global climate change, threat of global wars, and loss of sustainable systems have emerged to question whether life on Earth, so new, varied and fragile, will survive the primates who came to question how life itself came to be.