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.
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.
[---]
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 and hornworts, which still grow today in damp places like forest floors and stream edges. These plants did not have true roots or stems, and they stayed close to the ground. Fossils of early land plants, such as Cooksonia, date back to about 430 million years ago and show small branching stems only an inch or two tall.
- More Here
No comments:
Post a Comment