Phil Plait, the Bad Astronomer at Discover Magazine, describes the danger of asteroids are, then tells us how to keep them away from the Earth. Here's a hint: it does not involve the use of nuclear weapons. This is an entertaining and informative talk.
Ever wonder how it must have looked as clouds of space dust combined to form the Earth. National Geographic offers this awesome animation: Also from National Geographic, here's a theory of how some species of animals, but not large dinosaurs, survived the the aftermath of an enormous asteroid crashing into Earth. And here is a theory regarding the formation of the moon.
Click on this link to see a beautiful photo of the Earth by the Goddard Space Flight Center. What is stunning to me is the thin-ness of the Earth's precious atmosphere. Click on the image for a much-enlarged version.
How was this photo taken?
This spectacular “blue marble” image is the most detailed true-color image of the entire Earth to date. Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice, and clouds into a seamless, true-color mosaic of every square kilometer (.386 square mile) of our planet. These images are freely available to educators, scientists, museums, and the public. This record includes preview images and links to full resolution versions up to 21,600 pixels across. Much of the information contained in this image came from a single remote-sensing device-NASA’s Moderate Resolution Imaging Spectroradiometer, or MODIS. Flying over 700 km above the Earth onboard the Terra satellite, MODIS provides an integrated tool for observing a variety of terrestrial, oceanic, and atmospheric features of the Earth. The land and coastal ocean portions of these images are based on surface observations collected from June through September 2001 and combined, or composited, every eight days to compensate for clouds that might block the sensor’s view of the surface on any single day. Two different types of ocean data were used in these images: shallow water true color data, and global ocean color (or chlorophyll) data.
A few years ago, in a post called "Oil Tetris," I used the game of Tetris to illustrate the dangers of being dependent on petroleum and the fact that the United States consumes 5,000 gallons of gasoline per second.
Today, I am offering a similar set of images to illustrate my concerns regarding the dangers of overpopulation (and its attendant degradation and depletion of natural resources). As one who has pledged to support the 2010 GPSO effort, I am advocating that we directly and unflinchingly address the issue of whether we have overloaded our planet, our little lifeboat in outer space, with people.
Here's the general idea: If there were still only 2.5 billion people in the world (as there were as recent as 1950), it 
would be monumentally easier to sustainably tap into the world's resources to feed, house and clothe them. In 1950, it was not an empty world; 2.5 billion is a hell of a lot of people. Admittedly, it was not a peaceful world--it never has been a peaceful world, but it wasn't a world where so many basic critical resources were being stressed and exhausted (including water, oil, phosphates for fertilizer, food supply, ocean fishing and soil).
So here is the illustration. Back in 1950, the baseline for providing for 2.5 people was much lower than it currently is. There was room for error--room to make changes in the way the world was being run while still giving access for most people regarding most resources. Here is the world in 1950:
The falling pieces represent societal needs, and there was more ability to meet those needs in 1950. But now the world is a different place, where 2 billion people live on less than $2/day. It's a world where huge numbers of people are without water and sanitation. It's a world were valiant efforts are necessary to keep the food supply even stable, much less to increase it. Back in 1950, we could increase the food supply significantly, because we hadn't yet filled the world with 6.7 billion people and we hadn't yet planted virtually every square mile that could be planted. Now, many emergencies regarding resources require desperate responses that aren't often publicized by the Western media; knowing that there are billions of hungry people throws a damper on our annual Christmas-time consumerist orgy. That's how difficult it is for affluent Westerners to give a damn about the big picture, making it naive to suggest that we simply need to redistribute existing resources and continue packing greater numbers of people onto the planet. Nor is it easy to reason with many religions that find it utterly inconvenient to limit the ability of their members to "go forth and multiply."
There is little room for error these days, as represented by the following Tetris board:
The question, then, is whether it is responsible to run our world like a highly stacked Tetris board, where starvation already affects one billion people and yet we continue to add 1.5 million more people to our resource-challenged world every week. Is it wise to live so dangerously?
And for those who are tempted to comment that I should focus on things other than population, such as new technologies and social justice, by all means. I do that almost every week in my posts. But let's consider whether we would be better off also having the courage to address the basic issue of the carrying capacity of the planet.
Have you ever considered snugly wrapping a string around the entire Earth? If you did that, and then you added merely one additional meter of string (which would then raise the string uniformly off the surface of the Earth), how much higher off the ground would that new string be (the original long string, plus one additional meter)? Here's a simple statement of the problem, allegedly first used by Ludwig Wittgenstein. Here the math. Wonderful problem and surprising solution.