Long before dinosaurs roamed the earth, Earth was very different from the planet we know today. About 500 million years ago, most of the Earth’s surface was bare rock and dry soil. There were no trees, grass, or flowers. Life existed almost entirely in the ocean.
Then something amazing happened. Plants began to grow on land.
This moment was one of the most important events in Earth’s history, as it changed the planet forever. As a geoscientist, I am interested in flora and fauna, the changes in plant and animal diversity over time.
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The ancestors of plants lived in water
The story of plants begins with water. The earliest plant organisms were simple, small green life forms such as algae. Today, algae can still be seen as green slime on seaweed along the coast and on rocks in ponds.
Algae have lived in Earth’s oceans and lakes for more than a billion years. They can make their own food by making sugar using sunlight, water, and carbon dioxide. This process is called photosynthesis. As a byproduct, oxygen is released, a gas we need to breathe.
Initially, Earth’s atmosphere had little oxygen. For millions of years, photosynthetic organisms such as algae and some bacteria have slowly released oxygen into the air. This change, also known as the Great Oxidation Event, enabled the evolution of larger and more complex life. Without organisms that produce oxygen, animals, including humans, could never exist.
Scientists believe that the first true plants evolved from green algae about 470 million years ago. These early plants lived in shallow waters near coastlines where conditions frequently changed. Sometimes it was underwater, sometimes it was exposed to the air. This habitat helped them slowly adapt to life on land.
Getting ashore wasn’t easy. Aquatic plants are supported by water and can easily absorb nutrients, but land plants faced new challenges. How can I avoid dryness? How can you stand upright without floating? How do they get water and nutrients from dry ground?
To survive, early plants evolved important new features. One important adaptation was a waxy coating called the cuticle, which helps keep water inside the plant. Plants have also developed stronger cell walls that allow them to stand upright against gravity. Simple root-like structures called rhizomes anchored plants to the ground and helped them absorb water and minerals from the soil.
Early land plants were very small and simple. They are similar to modern liverworts, liverworts, and hornworts, and still grow in moist areas such as forest floors and river edges. These plants had no real roots or stems and were located close to the ground. Fossils of early land plants, such as Cooksonia, date back about 430 million years and show small, branching stems only 1 to 2 inches tall.
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Despite their small size, these plants had a huge impact on the earth. As plants spread over land, their roots helped break down rocks into soil. This is a process called weathering. This created rich soil that could support more life.
Plants also released more oxygen into the atmosphere, improving air quality and helping animals breathe. Plants created new habitats and food sources, allowing insects and other animals to migrate from water to land.
Complexity increases over millions of years
Once plants settled on land, evolution continued. About 420 million years ago, plants evolved vascular tissue, tiny tubes that carry water and nutrients throughout the plant. This adaptation allowed plants to grow taller and stronger because water could move upwards from the roots to the leaves. These vascular plants included early relatives of ferns and clubmoss.
With vascular tissue, plants really started to thrive. By about 360 million years ago, vast forests covered much of the Earth. Giant ferns and tree-like plants, some over 30 meters tall, dominated the landscape. Over time, dead plant material from these forests was buried and compacted, eventually forming coal, which people still use today as an energy source.
Another major step in plant evolution was the development of seeds found in seed ferns about 380 million years ago. Other seed plants, such as early conifers (the group that includes modern pine trees), can reproduce without the need for water for fertilization. Seeds protected the plant embryo, allowing the plant to withstand harsh conditions such as drought and cold.
The most recent major evolution of plants occurred about 140 million years ago, when flowering plants, which scientists call angiosperms, appeared. Flowers help plants attract animals such as insects and birds, and they spread pollen and seeds. A fruit developed to protect seeds and aid in their movement. Today, most of the plants we see, including trees, grasses, fruits, and vegetables, are flowering plants.
The first plants didn’t just survive. They changed the Earth. They changed the atmosphere, built the soil, and created ecosystems where animals could thrive on land. Thanks to the evolution of plants, Earth has become a green planet teeming with diverse life.
This edited article is republished from The Conversation under a Creative Commons license. Read the original article.
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