Earth Science: Biology – Evolution – The Evolution of Plants
The ancestors of today’s land plants lived in the oceans and seas. They had to develop features to meet challenges such as dehydration in order to adapt for survival on dry land.
Plants are able to create their own sustenance without feeding on other organisms. They use the process of photosynthesis to capture and use the sun’s light as an energy source. Plants are highly diverse in appearance, but most share characteristic structures such as leaves and roots.
Over the course of evolution, they have continually adapted themselves to prevailing environmental conditions. Fossil findings make it possible to distinguish four significant developmental periods in their evolution. Each of these resulted in a new diversification of plant life.
Around 460 million years ago, the first land plants evolved from aquatic green algae in the initial period of plant development. It is thought that the periodic drying up of bodies of water encouraged adaptations that prevented dehydration. Mod- ern plants such as mosses show examples of this transitional phase. They have a waxy layer that protects them from dehydrating in the open air.
During the next developmental stage, the first plants equipped with internal water conducting tissues emerged on coasts and other moist environments. Unlike mosses, these first vascular plants developed true roots and supportive stems, enabling them to obtain sufficient moisture outside an aquatic environment and to transport nutrients to all parts of the plant. The first seed-producing plants appeared during the third developmental period.
These differ from spore-producing vascular plants in that the embryo- together with a supply of nutrients-is encased in a shell: the seed. This led to the development of various kinds of plants without protective seed coverings—such as today’s evergreens—called gymnosperms. Lacking the encasement of fruit, their seeds fall freely to the ground to germinate. Seed- producing plants enjoyed significant advantages in the conquest of new environments.
They no longer depended on moist environments for reproduction and their embryos were more protected from adverse environmental conditions. Fruit-forming flowering plants called angiosperms, or plants with covered seeds appeared during the fourth stage of development about 130 million years ago. In contrast to gymnosperms, angiosperm seeds are sealed inside chambers, or ovaries.
The animals that eat the fruit end up transporting the seeds to different locations, which contributes to the enormous success of angiosperms.
BASICS
PLANTS ARE autotrophic (self- feeding) life forms. They provide the nutritional foundation for animals and humans who cannot manufacture their own food.