On October 13, 1994, the famous astronomer Carl Sagan was delivering a public lecture at his own university of Cornell. During that lecture, he presented the photo seen left. This photo was taken by Voyager 1 in 1990 as it sailed away from Earth, more than 4 billion miles in the distance. Having completed it primary mission, Voyager at that time was on its way out of the Solar System, on a trajectory of approximately 32 degrees above the plane of the Solar System. Ground Control issued a command for the distant space craft to turn around and, looking back, take photos of each of the planets it had visited. From Voyager's vast distance, the Earth was captured as a infinitesimal point of light (between the two white tick marks), actually smaller than a single pixel of the photo. The image was taken with a narrow angle camera lens, with the Sun quite close to the field of view. Quite by accident, the Earth was captured in one of the scattered light rays caused by taking the image at an angle so close to the Sun. Dr. Sagan was quite moved by this image of our tiny world. Below is an enlargement of the area around our Pale Blue Dot and an excerpt from the late Dr. Sagan's talk:
"We succeeded in taking that picture [from deep space], and, if you look at it, you see a dot. That's here. That's home. That's us. On it, everyone you ever heard of, every human being who ever lived, lived out their lives. The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam.
The earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity -- in all this vastness -- there is no hint that help will come from elsewhere to save us from ourselves. It is up to us. It's been said that astronomy is a humbling, and I might add, a character-building experience. To my mind, there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot, the only home we've ever known."
I feel that the late great Carl Sagans view is felt in this recent picture to the right of saturn. In this image from cassini you can see the earth on the left of saturns rings as a small dot just like in the images above.
Given these images it seems amazingly arrogant and egotistical of us to have a geocentric bound view of the universe. The universe is a fantastically vast place and for more than 13.699 billions years at least, it got by without humans. For about 10 billion years it got by without the earth. To think that we are somehow special and it was created for us is just absurd. We are just a cosmic grain of star dust in the vast stretches of the universe. When I contemplate such things like we are literally made of stars and that for the large portion of the universe no human at least on this planet was even in it, most of what the universe is made of (dark energy, dark matter), we don't know what it is but can detects its effects. The fact that everything on this pale blue dot I call home was created by a natural process of evolution with natural selection and that I share a common ancestory with everything else on the planet. All of this astounds me in such a way I can't describe. Who needs religion for awe and wonder. No thank you.
I have the real thing. Life, the universe and everything.
When Napoleon asked the physicist Laplace where God fitted into his model of the universe, the scientist’s answer was: “II ne me faut pas de cette hypothése-la” (I have no use for that hypothesis which you mention).
Gills consist of dense networks of thin-walled blood vessels over which water is pumped. This allows carbon dioxide in the blood to move into the water, and oxygen from the water to move into the blood.
The gills are arranged into a "counter current" system so the water flows through in the opposite direction to the blood. This means that oxygen will always be picked up via the blood, and carbon dioxide will always be picked up by the water.
The oxygen gets into the water in the first place in several ways. The most important sources are marine plants, which photosynthesise and produce oxygen as a by-product, and also oxygen from the air dissolving in the water.
The carbon dioxide entering the water, on the other hand, makes perfect plant food - the marine plants and plankton absorb it and, again using photosynthesis, turn it into sugars and oxygen
"It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition."