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Full Episode
Earth is the place we call home. It's where we work, eat, sleep and go about our daily lives. But how well do we really know it? We like to think of Earth as the blue marble, a stable, temperate world hospitable to life. But that's really just a snapshot of a dynamic and evolving planet.
If we zoom out on the cosmic timeline, we discover that our home would have been unrecognizable to us at most other times in its history. So, let's see if we can reconstruct what Earth might have looked like in the distant past. Let's imagine that alien scientists, who have never seen Earth as it is today, visited at various stages in its development.
Depending on when these visitors arrived, they would have formed completely different ideas about the kind of planet Earth was. What would they have seen 4.5 billion years ago? 2 billion years ago? Half a billion years ago? I'm Alex McColgan and you're watching Astrum. Join me today as we recreate Earth's ancient past and imagine what the planet might have looked like at various points in time.
Now, before we start, a little disclaimer. To answer these questions, we'll need to draw on some models that not all our scientists agree on. Travelling into the extremely distant past always carries some error bars. Some of the science we're pretty sure about. Other things are still being debated.
So, as we indulge our imagination, let's keep in mind that some of these claims are still being developed and rigorously questioned, as they should be. But to the best of our current knowledge, this is what our planet could have been like. As long as we're going into the past, we might as well go way back. Let's start 4.5 billion years ago. It's not the very beginning, but pretty close to it.
At this time, the Earth is basically a hot, viscous ball of molten rock, and I doubt our alien visitors will want to hang around for very long. The Earth is still young, not even 100 million years old yet, which in planetary terms is an infant.
Earth's thin atmosphere is made mostly of hydrogen and helium, most of which is stripped by the solar wind, since the Earth hasn't yet formed a magnetic field. As a result, the young planet has little protection from the sun's cosmic rays, and the planet is a hotbed of radiation. Earth is also constantly being bombarded with asteroids and comets, which add to its mass, a process called accretion.
Just imagine a big ball of chewing gum that you keep adding to with fresh wads of gum, and you'll get the idea. So not only is the young Earth hot and gooey, it's also growing. But these are not the only impacts the planet has to contend with. In the recent past, there was a cataclysmic event in which a protoplanet collided with the Earth, resulting in the formation of our Moon.
If our alien visitors were to see Earth in this state, would they see its potential? I'm unsure I would at this stage. But despite these ominous beginnings, the seeds of change are taking root. Riding aboard these inbound asteroids is a special compound that will play a crucial role in Earth's history – water.
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