Why Did Plants First Invade Land Around 470 Million Years Ago? — Here’s What Paleobotanists Found

Long before there were forests that spanned farther than the eye could see, the surface of the Earth was mostly made up of dry rocks and mud. Most of the green life that we are now accustomed to seeing on land was still living in water and the oceans. However, around 470 million years ago, during a period named the Ordovician period, some of these lifeforms managed to invade the land and became the very first versions of terrestrial plants over time.

The slow and quiet invasion of land by the aquatic plants would also eventually change our planet in ways that seem so impossible at first. Without them, there never would have been complex visible life on the surface of the Earth, let alone having forests and different animal species. But, how exactly were they able to transition from living on water to land? And why did they invade it in the first place? In this article, let’s look back at the history of our planet and find out how the first plants came to be and what impact they have on us.

How Fossils Reveal the First Plants on Land

The very first plants to live on the land surface of the Earth did not leave any old trunks or leaves that scientists were able to find. Instead, the discovery of when these invasions could have happened was estimated based on spores on rocks. Scientists found special fossilized spores, often called “cryptospores”, on rocks that were estimated to be around 470 million years old.

These findings are the oldest known fossil evidence that showcases plants moving onto land from their original habitat in water. However, these plants were not similar to the current ones we have on the planet right now, such as the plants with tall and leafy stems. Instead, they were probably moss-like, growing on the wet surfaces of ground near lakes, rivers, and shorelines.

Read more: Wikipedia

Why Moving Onto Land Helped Plants Thrive

When Life Moved To Land & The Disastrous Consequences | GEO GIRL

So, if for millions of years these plants were already living in water, why did they invade landmasses around 470 million years ago? Well, the ancestors of the very first plants on land were thought to be green algae living in fresh bodies of water like lakes and ponds.

Over time, these plant species learned how to live in the shallow parts of these environments, but these places are prone to being dried out, caused by changes in the climate of the planet. This created a scenario for these plants to begin moving onto land, as it is beneficial for their survival.

Once they were able to start living on land, even in just grounds near bodies of water, they were able to take advantage of several benefits. First, is that there is more access to sunlight as it is not blocked by water. This means that the plants that were able to live on land were able to make more food through photosynthesis.

The second benefit was the abundance of carbon dioxide in the atmosphere. The early plants used this feature to fuel their growth and further expansion into the land surfaces. Lastly, there were no other plants yet, or even visible complex life aside from some microbial lifeforms. In other words, there was less competition for resources. But their transition to land did not come without any dangers and risks.

How Early Plants Solved the Problems of Dry Land

When they left the water, the land gave them several benefits, but it also created serious challenges that they had to overcome to continue expanding and surviving on the vast land mass of the Earth. One of the problems they face is that the land could still dry out, and the early plants still needed some water to reproduce.

So, to survive, they had to evolve new features, such as the cuticle, which serves as an outer coating that helps hold water inside the plant’s tissues. It also provided them with some extra protection from the harsher sunlight that they are now receiving.

Another problem was that in the water, they could float freely and spread. However, on land, there are winds and moving landmasses that could displace them. So, over time, they develop a way to anchor themselves on the ground using tiny hair-like structures called rhizoids. These held them in place on rocks and land, even with the wind, and it also allowed them to soak up the moisture and minerals underneath.

Additionally, to reproduce, they also evolved tougher spores with walls that could survive being blown out by the wind and then landing in new environments. Over millions and millions of years, these early plant features set the stage for what would have become the complex parts of plants that we know of today, such as the roots, stem, and leaves.

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How the First Land Plants Changed Earth Itself

How Plants Caused the First Mass Extinction

When the first land plants successfully spread throughout the planet, they changed our world. The once barren and dried-out land was now home to complex visible life forms, instead of just microbial life. As these plants grew, their bodies trapped dust and helped break down the tough rocks.

Additionally, when they died, their remains mixed with the ground and, over a long period of time, it led to the formation of the first real soils capable of holding water and nutrients much better than rocks.

Moreover, the plants, as they evolved, consumed more carbon dioxide via photosynthesis and released oxygen to the atmosphere. This transition would have helped cool the planet and later allowed different animal species to live and breathe on land. Then, as plants continued to spread, they were able to create new habitats not only for themselves, but for different life forms to emerge and survive.

After tens of millions of years, what was once just a green, flat, tiny moss attached to rocks near bodies of water has now evolved to be the first small forests that would provide food and shelter for other forms of life, like insects, fungi, and eventually the different land animals.

Author's Final Thoughts

The first invasion of land by plants was not sudden and quick; instead, it took millions of years for the process to gradually happen and develop. It was a very slow step-by-step journey that started from green algae on fresh bodies of water, learning how to survive outside of it onto the rocks and ground, to simple plants spreading away from just the shorelines and wet areas.

Those early plants were very small, but their impact on our planet and the history of life is immense. Over a long period of time, their development led to the formation of the first true soils, the transformation of the atmosphere, and they made the Earth just an overall friendlier place for countless lifeforms to live in. Every forest, every garden, and every green habitat that we see today could be traced back to these first plants who have left the water around 470 million years ago.

Read more: Why Did Insects Grow So Huge Around 300 Million Years Ago — And What Made Them Shrink Again?

References & Further Reading

Wellman, C. H., Osterloff, P. L., & Mohiuddin, U. (2003). Fragments of the earliest land plants. Nature. https://doi.org/10.1038/nature01884

Gensel, P. G. (2008). The earliest land plants. Annual Review of Ecology, Evolution, and Systematics. https://doi.org/10.1146/annurev.ecolsys.39.110707.173526

Kenrick, P., & Crane, P. R. (1997). The origin and early evolution of plants on land. Nature. https://doi.org/10.1038/37918

Edwards, D., & Kenrick, P. (2015). The early evolution of land plants, from fossils to genomics: A commentary on Lang (1937) ‘On the plant-remains from the Downtonian of England and Wales’. Philosophical Transactions of the Royal Society B. https://doi.org/10.1098/rstb.2014.0343

Kenrick, P., Wellman, C. H., Schneider, H., & Edgecombe, G. D. (2012). A timeline for terrestrialization: Consequences for the carbon cycle in the Palaeozoic. Philosophical Transactions of the Royal Society B. https://doi.org/10.1098/rstb.2011.0271