Chapter 1: The Ediacaran Period and the Birth of Complexity

After approximately 4 billion years of gradual development, a pivotal surge of oxygen catalyzed the emergence of complex life on Earth. This marks the beginning of Part 42 in our exploration of Earth's history.

The Ediacaran Period (635 to 539 million years ago)

Metamorphosis

As previously discussed in Part 41, the Ediacaran signifies a dramatic turning point, marking the metamorphosis of life on our planet. Before this epoch, life was primarily microscopic; however, after the Ediacaran, it evolved into a more complex form. Much like a caterpillar transforming into a butterfly, life underwent a significant transformation.

But first, the planet faced another glaciation.

Approximately 579 million years ago, Earth experienced the Gaskiers Glaciation. Throughout our series, we've noted that following such glacial periods, a surge in carbon dioxide often leads to algal blooms, which subsequently generate oxygen and stimulate evolutionary advancements. This time, however, the pulse of oxygen propelled evolution to unprecedented heights.

Evolution was akin to an old dog mastering new tricks. As the planet thawed, it became home to large organisms for the first time, including peculiar seaweeds that reached heights of 30 centimeters—remarkably larger than any previous life forms.

New species emerged as well, such as Eoandromeda, a unique elliptical creature recognized as one of the first true animals.

So, how does oxygen play into this narrative?

Oxygen enhances metabolic processes. In its absence, if organism B consumes organism A, it gains merely 10% of the energy, and if organism C then consumes B, it drops to a mere 1%. This explains why bacteria typically do not consume one another. Conversely, with oxygen present, metabolic efficiency increases to 40%, making herbivorous and carnivorous lifestyles feasible. During the Ediacaran, we began to witness grazers and predators, along with the first intricate food chains.

But what triggered the sudden growth of organisms?

Predation encourages growth in both predators and prey; prey aim to grow too large to be consumed, while predators adapt by increasing their size to catch them. This initiated an evolutionary arms race, ushering in the Phanerozoic Eon!

Then, around 547 million years ago, the Baykonurian Glaciation occurred. This glaciation was notable, as it not only marked the transition between the Ediacaran and Cambrian Periods but also delineated the boundary between the Proterozoic and Phanerozoic Eons. There are only four Eons in Earth's history: Hadean, Archean, Proterozoic, and Phanerozoic, making this a significant milestone. The term Phanerozoic translates to "visible life," and this Eon will persist as long as complex life continues to thrive.

Chapter 2: The Cambrian Period and the Explosion of Life

The Cambrian Period (539 to 485 million years ago) continued the momentum established in the Ediacaran. Although oxygen levels dipped slightly, carbon dioxide concentrations soared to ten times those of today, and the planet was exceptionally warm with sea levels rising 50 meters higher than now. Evolution, which had already gained speed during the Ediacaran, reached an unprecedented rate.

During the subsequent 20 million years, known as the Cambrian Explosion, evolution surged faster than at any other time in history. This rapid change was partly due to the predator-prey dynamic, leading to the development of protective shells and skeletons. However, there was a deeper underlying cause.

Evolution thrives in unoccupied ecological niches. Previously, these spaces were filled by bacteria and microscopic life forms. The advent of complexity opened up entirely new possibilities and a fresh toolkit for evolution. It was a remarkable period in Earth's timeline.

Any animal with a structural mutation had a chance to flourish. Six legs? No issue. Segmented bodies? That works. Unusual worm-like shapes? Go for it. Snail-like creatures? Just be yourself. Today, around 30 basic animal body structures (phyla) exist. Our own phylum, Chordata, includes all vertebrates. Many, if not all, phyla emerged during the Cambrian Explosion, and they all originated in the oceans. By the end of the Cambrian, one frontier remained unconquered: land. That story comes next.

This article forms Part 42 of a 50-part series on Earth's history, each exploring a 100-million-year interval.

If you're interested in previous sections, you can find Part 41: THAW and look forward to Part 43: PLANTS AND FUNGI.

For a deeper understanding of Earth's evolution, check out the following videos:

This video titled "Earth's Evolution in 10 Minutes" offers a concise overview of the major milestones in the planet's evolutionary history.

The second video, "The Complete History of the Earth: Everything Before the Dinosaurs SUPER CUT," provides a comprehensive look at Earth's history leading up to the age of dinosaurs.