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What was the very first plant in the world? – Ivy, age 6, Phoenix
Long before dinosaurs roamed the land, Earth looked very different from the planet we know today. Around 500 million years ago, most of Earth’s surface was bare rock and dry soil. There were no trees, no grass and no flowers. Life existed almost entirely in the oceans.
Then something amazing happened: Plants began to grow on land.
This moment was one of the most important events in Earth’s history because it changed the planet forever. As a geoscientist, I am interested in changes in the diversity of flora and fauna – that’s plants and animals – over time.
Predecessors of plants lived in water
The story of plants begins in the water. The earliest plantlike organisms were simple, tiny green life-forms such as algae. You can still see algae today as seaweed along beaches or as green slime on rocks in ponds.
Early algae were just a cell or two in size and drifted in water.
NNehring/E+ via Getty Images
Algae have lived in Earth’s oceans and lakes for over 1 billion years. They can make their own food, using sunlight, water and carbon dioxide to create sugars. This process is called photosynthesis; it releases oxygen – the gas we need to breathe – as a byproduct.
At first, Earth’s atmosphere had very little oxygen. Over millions of years, photosynthesizing organisms like algae and some bacteria slowly released oxygen into the air. This change, sometimes called the Great Oxygenation Event, made it possible for larger and more complex life to evolve. Without oxygen-producing organisms, animals, including humans, could never have existed.
Scientists believe the first true plants evolved from green algae around 470 million years ago. These early plants lived in shallow water near shorelines, where conditions changed often. Sometimes they were underwater, and sometimes they were exposed to air. This habitat helped them slowly adapt to life on land.
Getting a foothold on dry land
Moving onto land was not easy. Water plants are supported by water and can absorb nutrients easily, but land plants faced new challenges. How would they avoid drying out? How could they stand upright without floating? How would they get water and nutrients from dry ground?
To survive, early plants evolved important new features. One key adaptation was a waxy coating, called a cuticle, which helped keep water inside the plant. Plants also developed stronger cell walls that allowed them to stand upright against gravity. Simple rootlike structures, called rhizoids, helped anchor plants to the ground and absorb water and minerals from the soil.
The earliest land plants were very small and simple. They looked similar to modern mosses, liverworts…
