400 million years ago, Earth was an alien world for fish

Space · Published 27 October 2026 Swipe more like this →

In short: Imagine a planet with no ice at the poles, rotating slower than today, and continents you wouldn't recognize. This was the Devonian period—a warm incubator where life underwent a radical transformation from the depths of the ocean to the first steps on land.

During the Devonian period, approximately 400 million years ago, the Earth's geography was unrecognizable by modern standards. The six continents and two large oceans we know today did not exist. Instead, the northern hemisphere was covered by a single vast ocean, and the climate was notably warmer than usual, characterized specifically by an absence of ice at the North Pole.

While the land appeared tranquil and alien—devoid of grass and dominated by strange tree-like structures rather than large trunks—the water told a different story. This era is famously known as the "Age of Fishes" due to an evolutionary explosion of aquatic species. However, these fish bore little resemblance to modern varieties, representing a unique branch of biological history.

The most significant shift occurred at the water's edge. The Devonian served as a critical transition point where early vertebrates began venturing onto land. One such creature, potentially a lungfish, represents the first tetrapods to leave the mud. This pivotal movement initiated an evolutionary transformation that would eventually lead to thousands of species, including humans, roughly 380 million years later.

The Devonian is essentially a prehistoric laboratory for terrestrial life. It was a period where small plants, shrubs, and mosses began to colonize a world still dominated by invertebrates like scorpions and large insects. By observing this era, we see the foundational mechanics of how complex life moved from aquatic environments to become the dominant force on land.

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