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Hank: After 2 years and nearly 9 kilometers, NASA's Curiosity Rover has finally reached its ultimate destination: Mount Sharp, a potential goldmine of Martian geological history. The mountain is basically a five-and-a-half kilometer high stack of rock layers, each recording a different chapter in Mars's environmental history.

NASA's saying that Curiosity's work here will be the sequel to its last big mission, the discoveries at Yellowknife Bay, which we told you about back in 2013. There, Curiosity found sedimentary rocks that had formed in PH-neutral fresh water, along with sulfate compounds that could have been used by ancient microorganisms as a source of energy, though obviously, it didn't find any direct evidence of life itself, which you probably would have heard about.

By now, the Rover is starting its ascent to the base of Mount Sharp and a feature known as the Murray Formation, which was probably deposited on an ancient lake bed. The Murray Formation is forty times thicker than the layer at Yellowknife Bay, potentially offering hundreds of thousands of years of Martian history, plus Curiosity is situated right where that formation meets another deposit that washed down the walls of Gale Crater eons ago. This means that it will have even more various different samples to study. Mission scientists say Curiosity will reach its drilling target in the next couple of weeks, and of course, you'll be able to find out about those results right here on SciShow Space.

Now, imagine what Earth would be like without life. That's what researchers at NASA's Astrobiology Institute recently did to create new guidelines in our search for alien life, and it turns out that we've been looking for the wrong clues, or, at least, the wrong combination of clues.

We look for signs of life on other worlds by using spectrometers which can detect chemicals present in the atmospheres of distant planets. And up until know we have been looking for compounds that tend to be created by life, like molecular oxygen which plants and some bacteria can produce via photosynthesis and ozone which forms when a third (3rd) oxygen atom binds with O2. We also look for methane which some micro-organisms can produce, most famously those that live in the guts or cows. The problem is all of these compounds can also be produced abiotically - without living things. So are these molecules really good indicators for the presence of life? To answer this question, researchers wanted to see how likely it was that these chemicals could be made abiotically and in enough abundance that we would be able to detect them from space.

To do that they made a model of what Earth's atmosphere would be like if there was no life, then they simulated what would happen to that fake Earth over time under different conditions, like what would happen if there had been different rates of volcanic activity which would change the atmospheres chemical composition. What if all the land and sea masses which react and absorb chemical from the atmosphere were distributed differently? And since energy from the sun is responsible for lots of reactions in the atmosphere what if levels of the sun's radiation were different?

In all, the researchers created fourteen thousand four hundred and ninety nine (14,499) different combinations of these factors simulating many hypothetical lifeless Earths, and many of those simulations ended up producing enough methane or oxygen or ozone to be detected across great distances. Suggesting that chemicals we have been looking for on their own aren't good indicators of life. However, none of the simulations ended up with detectable amounts of both methane and molecular oxygen, or methane and ozone. That's because those compounds are more, or less, mutually exclusive. Oxygen is apart of a complex chain of reactions that ultimately consumes methane in the atmosphere, so you wouldn't expect to find a large amount of both on a lifeless planet.

Scientists are discovering this relationship to be like college students and pizza, the two (2) just don't co-exist for very long because the college students are gonna consume the pizza, its just a force of nature. So if you are in a room that has a lot of college students in it, your not going to find a lot of pizza. But if you are in a room that has both plentiful pizza and lots of college students, there must be an ongoing supply of pizza coming from somewhere, which sounds great!

Anyway, the pizza in the metaphor is like the methane, if you have planets that have both methane and oxygen, like we have in Earths atmosphere, that means that those worlds must have consistent sources for both, like trees and alien cow butts. That combination is what we should be looking for, a discovery that might change the way we look for alien life.

Thank you for watching SciShow Space news, we here at SciShow rely in support from our viewers to keep making these things, to help keep exploring the universe and if you wanna help us out with that you can go to https://subbable.com/scishow. And don't forget to go to youtube.com/scishowspace and subscribe!

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