Chapter 3

CHAPTER 3

LET'S LOOK FOR ALIENS! WITH PROFESSOR CRUELLA CRACKLESNAP

IT'S ALL GOING PRETTY WELL, DON'T YOU THINK? We've found THOUSANDS of exoplanets all across the Galaxy- and lots of them seem pretty nice for life! CAN WE START LOOKING FOR ALIENS ON THEM? Well, yes... but we need to settle something first.

What do we actually mean when we say "'LIFE"? IT'S EASY TO THINK OF SOME LIVING THINGS (people, trees, and small angry gerbils are all forms of life). And IT'S EASY TO THINK OF SOME NON-LIVING THINGS (like a rock, or the planet Saturn, or your left shoe). But what actually makes a tree or a person ALIVE I, and a rock... I NOT ALIVE. WHAT ACTUALLY IS LIFE? It turns out, LIFE IS... COMPLICATED, and this question is actually pretty hard to answer.

There's the easy answer you learn in school, and the hard, real-life answer that scientists have to deal with. I'll explain the easy option first, then tell you why it's wrong. THE EASY ANSWER YOU LEARN IN SCHOOL SAYS THAT THERE ARE SEVEN THINGS YOU NEED TO BE CONSIDERED ALIVE: MOVEMENT (THIS ONE'S OBVIOUS... YOU HAVE TO BE ABLE TO MOVE AROUND) RESPIRATION (A FANCY WORD FOR BREATHING) SENSITIVITY (AN EVEN FANCIER WORD MEANING YOU FEEL WHAT'S GOING ON IN THE WORLD AROUND YOU) GROWTH (YOU GET BIGGER OVER TIME)

REPRODUCTION (YOU CAN MAKE SMALL BABY VERSIONS OF YOURSELF) EXCRETION (YOU GET RID OF WASTE- THIS MEANS GOING TO THE TOILET, NOT THROWING OUT YOUR TRASH) NUTRITION (YOU NEED FOOD) (This is a weird mix of fancy and non-fancy words, mainly picked so they spell the name of an imaginary old lady called MRS. GREN, which makes the list easier to remember during tests.)