We usually take our wonderful Earth for granted because we have known it all our lives, as have all humans who ever lived. Only a Big History sense of its distant past will leave us amazed and grateful and in this post, I will help us reflect on that.
In a nutshell, Earth were born out of a violent and improbably history where it could easily not have become what it is and there is no “we” to speak of, to do science, build cities, make art, write poems. Everything that has happened in our universe a long, long time ago seem destined to give us this perfect place to live.
Begin with the beginning, about 14 billion years ago when the Big Bang created space and time, and all kinds of matter The first three minutes of the universe after the Big Bang was a super-hot fireball with enormous temperature that expanded rapidly as it cooled down in what scientists refer to as hyper-fast “inflation”. That cooling started a whole chain of events that led to the formation of elements and matter and ultimately large structures like stars, galaxies and planets. Stars had, well a staring role in the process of forming our planet. Were it not for the massive explosion of stars known as supernovas, which took place when they have burned up all their hydrogen, there is no way the heavier elements trapped inside stars could be released to make planets or new stars.
Over billions of years, a long history of successive supernovas contributed more and more heavy elements to the galaxy to the point where it contained enough heavy elements for rocky planets to form. That was the situation 4.5 billion years ago, the time when our solar system, the Milky Way, and Earth came into being. The late American astronomer liked to say that we are made of stardust. He is right.
And Earth could not exist without the Sun, itself a star. That much is obvious. What is less obvious is just how run-of-the-mill ordinary our Sun is. To be more specific, the Sun is just one of about 10,000,000,000,000,000,000,000 stars altogether. And yet, it bright and hot star has to be of the exact distance from Earth, no more and no less. Any closer, the Earth would be incinerated. Any further away, Earth would be a frozen planet unsuitable for life as we know it.
Then, there’s our Moon which often plays second fiddle compared to the Sun in discussions of Earth’s liveability. But consider this: Earth is the only solar system planet that has one moon. We might have had no moon, two moons, or a moon that orbited backward, leading to very different human situations, or no humans at all!
We should be grateful to the one Moon we have, for it plays a critical part in the human situation. The Moon stabilizes Earth’s motion, generate the tides that help marine animals adapt to life on land, keep most nights from pitch darkness, provide romantic evenings for young peoples, help people construct calendars and so on.
For all its romantic associations, our Moon had a darker, rougher side to it – its face is pockmarked with craters big and small that came from the giant impact of cosmic debris over billions of years. In fact, the Moon itself was formed from such impact. As smaller planets hit larger ones at just the right distance between centre and rim, it will tear away a huge portion of the larger planet, sending debris into a disk surrounding the larger one, a disk that gradually pulls together into a satellite. The Moon is one such satellite. Earth must have received the same cataclysmic treatment after formation of the Moon, but we were lucky enough to escape being torn apart and scattered like debris into space.
With all the “right conditions”, Earth was able to develop into a much quieter, better-behaved place, a place so liveable that, as I mentioned before, we take it for granted, oblivious to the many miracles that made it so.