Lunar Eclipse

It's been there a while, the Moon. As to where it came from, the current theory is often referred to as ‘the Big Whack’. Astronomers are by now well versed in this type of endearing shorthand. Beginning of the Universe? ‘Big Bang’. A very large star, that happens to be red? ‘Red giant’. Vast swathes of non-luminous material, making up a large part of the Universe? ‘Dark matter’. You get the drift.

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Anyhow, this Big Whack. Allegedly, way back in the early days of the story of the solar system, the young Earth was smacked full on by an object the size of Mars. That's pretty big; half the size of Earth, in fact. The part of the Earth that was smashed into smithereens by the giant impact first fell into orbit about the Earth and then fell under its own gravitational impetus to effectively re-form as the Moon.

This kind of thing is known as a giant impact hypothesis. These hypotheses have been very popular since they found a massive crater in the Gulf of Mexico in the 1970s, which they think is the ‘smoking-gun crater’ of the cometary impact that may have caused the extinction of the dinosaurs. Since then, giant impact hypotheses have been popular.

The early life of the solar system was dominated by giant impacts. There were so numerous that those times are known as the period of ‘late heavy bombardment’. Each giant impact must have obliterated all life that had developed on Earth up to that point; the severity and frequency of the impacts would have been so great that nothing would have survived. Astronomers rather cutely call this ‘the impact frustration of life’, suggesting that each giant impact was a ‘massive extinction event’, in which all or most of life on Earth would have been wiped out.

For convenience of study, we divide the Earth’s 4.5 billion year history into epochs punctuated by major events such as mass extinctions. Some of those — such as the mass extinction event about 250 million years ago — were truly catastrophic, with up to 96% of all marine species being wiped out. The time is known as ‘the Great Dying.’ (See, they’re at it again.)

And what about life out there in the Universe? If evolution is universal (and if life on planet Earth is just one example of a pattern of impact catastrophes and extinction events) then life on other planets will have to be equally tenacious to survive.