The ocean, in this light, is like an alien world within our own. Many of its creatures are still unknown to us — both in kind and number. Their behaviors and adaptations remain inexplicable. Even the very contours of this world are still unmapped: We probably know more about the surface of Mars than we know about the ocean floor.

Understanding the sea is to understand our planet better, at a fundamental level. “There’s so much about how the planet works that is basically preserved in this sort of underwater museum,” Vicki Ferrini, senior research scientist at Columbia University, told Vox’s Mandy Nguyen last year.

But not only is the ocean a source of mystery, it’s also a place of adventure. On Unexplainable — Vox’s podcast about big mysteries and all the things we learn by investigating the unknown — we’ve been talking to the scientists who have gone on journeys to understand this watery realm. They’ve come across fearsome creatures like the giant squid, conducted forensic investigations of mysterious deaths, visited octopus cities, and ventured down as deep as humanly possible.

Since the dawn of humanity, we have looked questioningly to the heavens with great interest and awe. We’ve called on the stars to guide us, and have made some of humanity’s most interesting discoveries based on those observations. This also led us to question our existence and how we came to be in this moment in time.

That journey began some 14 billion years ago, when the Big Bang led to the universe emerging from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, they spawned galaxies, stars, planets, and eventually, life.

In the above visualization, Pablo Carlos Buddassi illustrates this journey of epic proportions in the intricately designed Nature Timespiral, depicting the various eras that the Earth has gone through since the inception of the universe itself.

Evolutionary Timeline of the World

Not much is known about what came before the Big Bang, but we do know that it launched a sequence of events that gave rise to the universal laws of physics and the chemical elements that make up matter. How the Earth came about, and life subsequently followed, is a wondrous story of time and change.

Let’s look at what transpired after the Big Bang to trace our journey through the cosmos.

The Big Bang and Hadean Eon

The Big Bang formed the entire universe that we know, including the elements, forces, stars, and planets. Hydrogen and massive dissipation of heat dominated the initial stages of the universe.

During a time span known as the Hadean eon, our Solar System formed within a large cloud of gas and dust. The Sun’s gravitational pull brought together spatial particles to create the Earth and other planets, but they would take a long time to reach their modern forms.

Archean Eon (4 – 2.5 billion years ago)

After its initial formation, the surface of the Earth was extremely hot and entirely liquid. This subsequent eon saw the planet cool down massively, solidifying some of the liquid surface and giving rise to oceans and continents, as well as the first recorded history of rocks.

Early in this time frame, known as the Archean eon, life appeared on Earth. The oldest discovered fossils, consisting of tiny, preserved microorganisms, date to this eon roughly 3.5 billion years ago.