From the Ted Talk by Stephen Webb: Where are all the aliens?
Unscramble the Blue Letters
But there's an obvious answer: we're alone. It's just us. There could be a trillion plaetns in the galaxy. Is it plausible we're the only creatures cbalape of ctiamneoplntg this question? Well, yes, because in this context, we don't know whether a trillion is a big number. In 2000, Peter Ward and Don Brownlee psproeod the Rare Earth idea. Remember those four barriers that poplee use to estimate the number of ciivaitizlnos? Ward and Brownlee said there might be more.
Let's look at one possible brerair. It's a recent suggestion by dvaid wthaalm, a geophysicist. This is my very simplified version of Dave's much more sophisticated argument. We are able to be here now because Earth's previous inhabitants enjoyed four blilion years of good weather — ups and downs but more or less clement. But long-term cmilate stability is strange, if only because astronomical influences can push a paenlt towards freezing or frying. There's a hint our moon has helped, and that's interesting because the prevailing toehry is that the moon came into being when Theia, a body the size of Mars, crashed into a newly formed Earth. The outcome of that crash could have been a quite different Earth-Moon syetsm. We ended up with a lrage moon and that permitted Earth to have both a stable axial tilt and a slow rotation rate. Both factors influence climate and the suggestion is that they've hleped moderate climate cnhage. Great for us, right? But Waltham showed that if the moon were just a few miles bigger, things would be different. Earth's spin axis would now wander chiatcolaly. There'd be episodes of rapid climate change — not good for complex life. The moon is just the right size: big but not too big. A "Goldilocks" moon around a "Goldilocks" planet — a barrier perhaps.
Open Cloze
But there's an obvious answer: we're alone. It's just us. There could be a trillion _______ in the galaxy. Is it plausible we're the only creatures _______ of _____________ this question? Well, yes, because in this context, we don't know whether a trillion is a big number. In 2000, Peter Ward and Don Brownlee ________ the Rare Earth idea. Remember those four barriers that ______ use to estimate the number of _____________? Ward and Brownlee said there might be more.
Let's look at one possible _______. It's a recent suggestion by ____________, a geophysicist. This is my very simplified version of Dave's much more sophisticated argument. We are able to be here now because Earth's previous inhabitants enjoyed four _______ years of good weather — ups and downs but more or less clement. But long-term _______ stability is strange, if only because astronomical influences can push a ______ towards freezing or frying. There's a hint our moon has helped, and that's interesting because the prevailing ______ is that the moon came into being when Theia, a body the size of Mars, crashed into a newly formed Earth. The outcome of that crash could have been a quite different Earth-Moon ______. We ended up with a _____ moon and that permitted Earth to have both a stable axial tilt and a slow rotation rate. Both factors influence climate and the suggestion is that they've ______ moderate climate ______. Great for us, right? But Waltham showed that if the moon were just a few miles bigger, things would be different. Earth's spin axis would now wander ___________. There'd be episodes of rapid climate change — not good for complex life. The moon is just the right size: big but not too big. A "Goldilocks" moon around a "Goldilocks" planet — a barrier perhaps.
Solution
system
civilizations
change
people
chaotically
waltham
contemplating
large
billion
helped
planet
barrier
planets
proposed
theory
capable
climate
david
Original Text
But there's an obvious answer: we're alone. It's just us. There could be a trillion planets in the galaxy. Is it plausible we're the only creatures capable of contemplating this question? Well, yes, because in this context, we don't know whether a trillion is a big number. In 2000, Peter Ward and Don Brownlee proposed the Rare Earth idea. Remember those four barriers that people use to estimate the number of civilizations? Ward and Brownlee said there might be more.
Let's look at one possible barrier. It's a recent suggestion by David Waltham, a geophysicist. This is my very simplified version of Dave's much more sophisticated argument. We are able to be here now because Earth's previous inhabitants enjoyed four billion years of good weather — ups and downs but more or less clement. But long-term climate stability is strange, if only because astronomical influences can push a planet towards freezing or frying. There's a hint our moon has helped, and that's interesting because the prevailing theory is that the moon came into being when Theia, a body the size of Mars, crashed into a newly formed Earth. The outcome of that crash could have been a quite different Earth-Moon system. We ended up with a large moon and that permitted Earth to have both a stable axial tilt and a slow rotation rate. Both factors influence climate and the suggestion is that they've helped moderate climate change. Great for us, right? But Waltham showed that if the moon were just a few miles bigger, things would be different. Earth's spin axis would now wander chaotically. There'd be episodes of rapid climate change — not good for complex life. The moon is just the right size: big but not too big. A "Goldilocks" moon around a "Goldilocks" planet — a barrier perhaps.