We really are isolated here in our little “pale blue dot” (as Carl used to call Earth), but we have been slowly teaching ourselves the Cosmos through observation.

It has been 400 years since Galileo first saw Venus through his telescope, and since then, we have already observed and identified tons of celestial bodies—such as red giants, white dwarfs, nebulae, pulsars, you name it! Objects that are so big and so far away that we can but observe in wonder. Nonetheless, we are clever creatures, and we have learned a great deal about the Cosmos—despite the astronomical distances.

However there are still many mysteries that we haven't solved, for example, we suspect there are other forms of matter and energy out there that we still can't even comprehend—and we resort to call them “dark”³. Furthermore, we are not sure why we haven't found other forms of life, statistically the Universe should be brimming with life! So where is everybody?... We don't know, as Carl said, “we are standing at the shores of the cosmic ocean...” and we have barely dipped our ankles.

We started dipping our feet in the cosmic ocean thousands of years ago, thanks to our curiosity. One of the first people to think deeply about where he was standing, was Eratosthenes, 276 BCE⁴. He was the first person to propose that the Earth was not flat. He came up with this crazy idea just by looking at the length of the shadows casted by two sticks. The catch is that these two sticks were in two different cities, with different latitudes. Eratosthenes noticed that in a certain day of the year, one of these sticks (the one located farther from the equator) casted a shadow of a certain length, while the other one (closer to the equator) didn’t have a shadow at all.

Any other person would have missed this detail, but Eratosthenes was a badass! And with this piece of information, and a little geometry, he calculated the diameter of the Earth—quite accurately for a man born almost 2300 years ago.

Eratosthenes lived in Alexandria, one of the first civilizations who challenged our knowledge of the universe through scientific observation. In this city, founded by Alexander the Great, amazing scientific advancements happened thanks to Alexander’s appetite for knowledge and curiosity. Every ship that docked in Alexandria was searched—not for contraband, but for books. These were copied, stored in the Great Library of Alexandria, and returned to their owners.

Many disciplines like mathematics, mechanics, geometry, language, and astronomy, were seriously developed in Alexandria’s first 300 years—before it fell under Roman hands around the year 48 BCE. Its downfall, other than religious siege and other political issues, was that they kept all this knowledge in a single library, only available to the elite and the rich. This separation of the rich and the poor obviously led to a revolt that destroyed the library, burning most of the scientific discoveries made back then.

Yes... their cultural inequality was their downfall, but it was a fair try for a young and inexperienced civilization.

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Chapter 2: Where do we come from?

Alright so humans have lived for less than a million years, and the Earth is 4.2 billion years old. OK... But how did life originate?

The origin of life is very hard to identify—the concept itself is even difficult to grasp. What is life anyway? Let me remind you that we are just a collection of organic molecules who seem to have a desire to replicate ourselves. That’s the most fundamental drive of living organisms, reproduction.

In fact, life on Earth seems to have originated this way, about 4 billion years ago, when certain carbon‑based protein molecules replicated themselves (for some bizarre reason). As they replicated, the environment around those molecules shaped them, making slight changes depending on the things these molecules experienced during their life. As generations went by, they became more adapted to their environment and a little more skillful at replicating themselves.

This skill‑shaped replication, based on the environment, happened all around the young Earth, and as they became more complex, and more specialized, the molecules that were good at a particular task found synergy with others—so they grouped to form a cell.

Once these small pieces were confined within a cell, the different sections took different tasks. The nucleus took charge of all the logistics of replication, the mitochondria took charge of the energy production, the cell wall took the role of a protective layer, etc. And they started replicating all over the place!

A couple billion years went by, and these little cells realized that if they used half of their “replication juice” (shaped by their own environment) and merged it with half of someone else’s “replication juice” (shaped perhaps by a slightly different environment), their offspring would have a better chance of survival. The broader the survival information is, the better. That is precisely what sex is, and seems to have been invented around two billion years ago.

Obviously, when I say “they realized” or “invented” of course I don't mean it, this wasn’t a conscious effort it was simply what worked best, and survived the most. Natural selection.

It’s important that we pay attention to the timeline, this process took a long freaking time! About 2 billion years of sexless unicellular organisms struggling to adapt, and almost another 2 billion years of sexual (but still) unicellular organisms. But then...something remarkable happened: around 600 million years ago, the cells started grouping together to form even bigger organisms. Making the first multicellular organisms.

Once the cells learned to group together, another 100 million years went by and a bunch of creatures (visible to the naked eye) like the trilobites were all over the ocean floor. This event was called the Cambrian Explosion. And I guess they named it “explosion” since for 4 billion years life was exclusively unicellular, while it took 2% of that time to produce a vast variety of multicellular organisms. But don't forget: 100 million years is a long freaking time! Certainly NOT an explosion…

Explosion or not, this event led to hundreds of millions of species that lived and flourished across the millennia. Fast forward to about ten million years ago and the first creatures resembling a human started appearing. This was all thanks to the long process of evolution and natural selection.

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