You've heard that, right? Life is a mixed blessing. For every up, there's a down. It's like a roller coaster ride:
Unfortunately, though, sometimes the low point in life -- the bottom of the roller coaster swoop -- can be terminal. And not just for the individual person, but for a whole family, town, civilization -- or even for thousands of species all at once.
The graph above shows the estimated percentage of marine species lost during major extinction events over the last 500+ million years.
We, the human race, were lucky that our mammal ancestors survived the K-T, the Cretaceous–Tertiary extinction event, which occurred approximately 65 million years ago. If they hadn't, we wouldn't be here.
That was the last really large extinction event.
You'll notice, though, that these things happen periodically; not on a regular basis, but every so often, and somewhat predictably. Most of them result from impacts of asteroids or comets. And guess what -- those "planet killers" are still out there.
We can state with absolute certainty that another large impactor will be on a collision course with Earth at some point in the relatively near future. It could be a hundred years from now, a thousand years, a million years, ten million years -- or it could be, metaphorically, tomorrow.
Thousands of near-Earth objects (NEOs) are in orbits that bring them into close proximity with the Earth. In addition, there are millions of icy and rocky objects out in the Kuiper belt, any one of which could be jostled from its orbit and sent plummeting toward the Earth at any time. It is estimated that at least 70,000 of these objects are more than 100 km in diameter, large enough to cause the next major extinction event.
We saw just a few weeks ago what can happen out of the blue, as it were, unpredictably, when a very large object, probably a comet, slammed into Jupiter. No one saw this coming, and the scar the impactor left on Jupiter was as large as the Earth.
An organized and comprehensive effort to find, catalog, and track these objects ought to be a high priority for us vulnerable Earthlings. For various reasons, though, we're not yet doing all that we should:
Existing sky surveys miss many asteroids smaller than 1 kilometre across, leaving the door open to damaging impacts on Earth with little or no warning, a panel of scientists reports. Doing better will require devoting more powerful telescopes to asteroid hunting, but no one has committed the funds needed to do so, it says.
To get a sense of the damage these chunks of rock and ice can do when they hit home, take a look at this collection of "Asteroid Impact Craters on Earth as Seen From Space." Here are just two of the amazing images you can see:
The search for NEOs can be conducted at relatively low cost, especially if it's done on a cooperative international basis and involves government, academic, and individual volunteer efforts.
Although the odds of detecting and stopping a major comet or asteroid that could threaten civilization are small, they are greater than zero, and the cost of ignoring the search is, well, potentially everything.
Roller coaster rides are fun. But when the survival of human -- and posthuman -- civilization is at stake, it's imperative that we set a high priority on detecting and then deflecting the next planet killer before it gets here.