Why do we get used to smells?

The city people out there, might wonder why the heck farmers get used to that "countryside" smell. Although our nervous system has evolved to become progressively less sensitive to a stimulus (in this case a smell). This enables us to concentrate more on the new sights/smells that might pose more of a "danger" to us. We also have what's called an olfactory memory that discards smells that we've experienced recently - so you don't notice the smell of your house when you come back from work, but it smells different when you come back from your holiday!

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Mars' atmosphere was "oxygen rich"

Scientists at NASA have discovered using their Spirit Rover that Mars once had an oxygen rich atmosphere 4 billion years ago. This was 1,500 million years prior to the formation of earth. The scientists came to this conclusion because they had analysed samples that the Spirit Rover had collected, they also compared these samples with Martian meteorites that have crashed into earth. The Scientists then were able to examine the composition of the meteorites and the samples collected, they then discovered a high percentage of oxygen. Also  Mars' distinct red colour, shows evidence of a process called oxidation, which obviously as the name suggests needs a high quantity of the oxygen. It is likely that the Red Planet was warm, wet and rusty, billions of years before Earth's atmosphere became oxygen rich, enough for life to develop on Earth. 

This could mean that life did exist on Mars, and it could mean that at some point we could end up living on Mars!