Prehistoric time team- The Pre-Cambrian…Molten! Hot! No Life! The first Life! Huge Ice age! And More!

9 Mar

Folowing our trip to the land of the giant bugs (The Carboniferous) let’s activiate the imaginary time machine again…and go back…Go on, push the lever. Let’s go back as far as we can in Earth’s history, or as far back to when we can land on it….this could be fun. Don’t push that lever back too far though!

We’re about to visit a truly alien world.

You see, it’s one thing having a moan about creepy crawlies and then seeing what giant bugs used to exist in prehistory, but it’s quite another when some people complain about the weather or the potential of global warming or even the mess that is world politics. Imagine then, if you will…a world not just without any politics (and therefore no people), but without any life.

So we’re back in the time machine again, which I’ve decided is a cosy globe like affair, with built in sofa and reinforced windows. We need the windows, as we won’t be going outside. Hell no!

I told you not to touch that lever quite so far. As it is, you’ve sent us back roughly 4 billion years. We could go back further, or sooner, but the view would be much the same. Scientists call this the ‘Hadean’ eon (and yes, it’s named after Hades from Greek mythology), and is the earliest geological eon time period. It’s very hot out there, and there’s absolutely no life. It’s a molten, meteorite bombarded hell fest out there, my friend. Incidentally, a vast measure of time such as an eon relates to geological formation, rather than life, such are the vast expanses of time.

For most of its existence Earth looked like this. HOT!

Ok, just pulling a few levers and pressing a few buttons here; you might feel a bit queasy. We’re going forward in time some considerable distance.

Look at that- active volcanoes everywhere and the sky is an uncanny orange colour (see below). We’re now somewhere in the Archean eon (Greek for “beginning”) The Archean eon is a geological time scale that lasted from about 3800 million to 2500 million years ago. I hope you’re following all this. Don’t even think about how many weeks that is, you might implode. It is split up into four eras, but we could arrive at any point in any of them and the view would be similar. It was three times hotter at the beginning of the eon than modern day Earth, which is very hot indeed, but things are cooled a bit in the time we’ve arrived. Some of the oldest visible rock on modern Earth is from the Archeon, the nearest to us Brits being in Scotland.

It's another world...lonely, orange skied and inhospitable to humans (which is an oxy-moron, as there couldn't have been any).

Anyway, we’re staying indoors for this trip, so we’ll have to just look through the windows. Yes, that is an expanse of water in the distance…The shallow seas look a bit unhealthy, but that green tinge is caused by dissolved iron.  I could tell you what the era names are, but to be honest they wouldn’t mean much to us. It’s all about the development of rocks at this point, and not much else by the looks of things, which could be a fascinating subject in itself though. Oi, what are you rolling your eyes for, you’re thousands of millions of years in the past. This is impressive! We can’t see any obvious signs of life, that’s for sure. The earliest discovered life is from the second of these eras…ooh. The cobble like structures are thromobites, and they’re formed in shallow water by micro organisms. How are they formed? Well, now you’re asking…I can tell you about the climate, which is temperate despite all the volcanic volicity.

It’s a beautiful lonely world out there.

So, we’ve just travelled unimaginable distances of time, cutting a swathe through a good two thirds of the Earth’s existence. If you think that timescale is scary, have a think about the age of the universe. Astronomical observations have cited this age to be 13.7 billion years. Scientists are also prophesying events trillions of years into the future, but let’s stick with more earthly considerations for now.

Cryogenian Earth- Global Snowball for millions of years.

Push that lever there, we’re off to the next eon- the Proterozoic (Greek for ‘earlier life’), Here the atmosphere has 100 to 1000 times the Carbon Dioxide than modern levels. It’s life (or less of it), Jim, but not as we know it. We could go out for a walk, but er…let’s not eh? Not without a special suit anyhow, otherwise it’d be an extremely short, deadly excursion.

Interestingly, about 2000 million years ago a sudden event called the “Oxygen Catastrophe” occurred, when oxygen-producing photosynthesizing single-celled organisms evolved. They used light to fuel their life cycle, like plants. The result of this huge and sudden oxygen rise was that all the exposed iron on the planet rusted, leaving behind iron bands in the geological record. What was even more shocking for the first Earth life, was your outlook if you were not used to oxygen. Extinction loomed.

Then, some (considerable) time later the Earth was hit by an ice age which makes the last one look like a gentle snowfall in comparison. You wouldn’t have put much money on anything surviving. Coming at the end of the Proterozoic eon, this is known as the Cryogenian age (Greek: “Cold birth”), such was the severity and extent of the ice. The only life that survived was secret and small and we would be hard pressed to find it. The microscopic ancestors of fungi, plants, animals and kelps all evolved during this time- so, how about that eh? It’s not all bad news! You look like you’ve seen enough though, or perhaps your pale expression is having to compute the vast timescales where a lot happened, but not much happened on a daily basis in the way we’re used to (ie: nothing resembling advanced life did anything on Planet Earth, for 4000 million years).

So that has been 4000 million years of pre-history in one blog; most of the Earth’s history! It’s a whistle stop tour!

But things are looking up for Planet Earth. Fast forward to the future, but not so fast or so far this time.

Next stop- The Cambrian…and visible, active LIFE!


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