Where on Earth did the water come from?

Earth's supply of water is incredibly important for its ability to sustain life, but where did that water come from? Was it present when Earth formed or was it delivered later by meteorites or comets from outer space?

The mystery of the small dimensionless number with a big effect

Non-dimensional numbers may sound like a scary, incomprehensible term reserved for scientists in a laboratory, but you have more experience with them than you know. The Mach number measures the speed of an object relative ...

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