A Quote by Neil deGrasse Tyson
This influential, yet controversial idea requires that the mixture of species on Earth at any moment acts as a collective organism that continuously (yet unwittingly) tunes Earth's atmospheric composition and climate to promote the presence of life... But I'd bet there are some dead Martians and Venusians who advanced the same theory about their own planets a billion years ago.
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Consider: Life arose on Earth close to four billion years ago. Four billion years of slithering, swimming, and soaring life forms. But only in the last 200 thousand years has a species arisen that can fathom the laws of nature and build hardware able to signal its presence.
I'd bet almost anything that life from another planet, if formed independently from life on Earth, would be more different from all species of Earth life than any two species of Earth life are from each other.
All indications are that three and a half billion years ago, Mars looked like Earth. It had lakes. It had rivers. It had river deltas. It had snow-capped peaks and puffy clouds and blue sky. Three and a half billion years ago, it was a happening place. The same time on Earth, that's when life started. So did life start on Mars?
Our planet has been around only for four and a half billion years. Let's imagine a planet that has life on it such as life is on Earth and it's seven billion years old. Let's say that planet evolved intelligence. Well, that intelligence would be way more advanced than what we call intelligence here on Earth. How long has intelligence been around on Earth as we've come to define it?
We're being challenged to do something so profound, it's unprecedented in the history of our species, and there couldn't be more at stake. It's not even our species at stake; it's the whole dream of life on earth that's taken 4.5 billion years to realize - all this beautiful pastoral life on earth.
The Earth has been lawned with life for something over 3.5 billion years. That's a span of time great enough to encompass some honest-to-goodness catastrophe. For example, 700 million years ago, Earth underwent a planet-wide deep freeze, with ice covering the oceans from the poles to the equator.
We are the intelligent elite among animal life on earth and whatever our mistakes, [Earth] needs us. This may seem an odd statement after all that I have said about the way 20th century humans became almost a planetary disease organism. But it has taken [Earth] 2.5 billion years to evolve an animal that can think and communicate its thoughts. If we become extinct she has little chance of evolving another.
Here on Earth, we're exposed to asteroids hitting the Earth, eventual changes in the Sun, changes in the Earth's climate, things we're doing to the Earth's climate. If we want to survive, we need to become a multi-planet species. That's further down the road, but the first wave is going to be the explorers.
In view of the immense power of natural weather and climate fluctuations and the great buffering capacity of the Earth, especially the ocean, it is easy to be skeptical about whether small anthropogenic changes of atmospheric composition can have important practical impacts.
About two million years ago, man appeared. He has become the dominant species on the earth. All other living things, animal and plant, live by his sufferance. He is the custodian of life on earth, and in the solar system. It's a big responsibility.
One in 200 stars has habitable Earth-like planets surrounding it - in the galaxy, half a billion stars have Earth-like planets going around them - that's huge, half a billion. So when we look at the night sky, it makes sense that someone is looking back at us.
Every creature alive on the earth today represents an unbroken line of life that stretches back to the first primitive organism to appear on this planet; and that is about three billion years.
The record of the rocks contains very little, other than bacteria and one-celled plants until, about a billion years ago, after some three billion years of invisible progress, a major breakthrough occurred. The first many-celled creatures appeared on earth.
You see, every creature alive on the earth today represents an unbroken line of life that stretches back to the first primitive organism to appear on this planet; and that is about three billion years.
For all we know, the aliens have already done this and unwittingly concluded that there was no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility would be if aliens had become aware of the technologically proficient species that now inhabits Earth, yet they had drawn the same conclusion.
The concentration of atmospheric carbon dioxide has changed greatly since fossilized life began on Earth nearly 600 million years ago. In fact, there is only 1/19 as much CO2 in the air today as there was 520 million years ago. That high CO2 was hardly the recipe for disaster.
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