Plant evolution (Click to select text)

Plant Evolution A long 3000 million years ago the earth was not suitable for life as the atmosphere contained little to no oxygen and without this, deadly ultra violet rays from the sun bombarded the unprotected surface. This lead to life beginning in the ocean where it was safe from the sun's rays. It was here that life began with bacteria and small microscopic plants, called algae. Algae is the worlds oldest known fossil. Found in rocks of South Africa and Central Australia up to 3100 years ago. The Age of Algae lasted more than 2000 million years old, which is about half of planet earth's lifetime. During this long period of time, some of the algae developed the ability of being able to make food by using the energy from sunlight to converts carbon dioxide and water into sugar or starch. This process was called photosynthesis. The next stage in the development in plants was 'The Age of Primitive Vascular Plants. This new period (the second stage) in plant history occurred within the next 50 million years (400-500 million years ago). Some of these developed root systems stems and leaves. They also formed woody tissue, which created stiffer stems, which eventually developed into tree trunks. They became tree-like and up to 40 meters tall, forming the world's first forest. 'The Age of Seed Bearing Plants' was the next stage of plant history where plants were taken to their next step up in the evolution. This occurred around 280 million years ago. This was also the dinosaur era. Earth began to become a lot drier, and these plants began to adapt to the ever so changing climate. These plants developed the ability to produce seeds to reproduce their new generations. The advantages of this was that these seeds were able to survive dry periods, even long droughts and then germinate and grow when moisture became available. Last but not least we have 'The Age of Flowering plants' beginning just over 100 years ago this was the fourth and last leap forward in the development of the world's plants. Unlike flowering plants cycads and conifers relied on winds to dispense pollen from male to female cones, the flowering plants attracted insects and birds to move pollen from males to females. The first flowering plants to evolve seemed to be the palms, however soon after many others followed. These gradually became more numerous then plants that had existed before. These developed into many different shapes and sizes from tiny little wild flowers, to huge oak and gum trees. Their seeds are enclosed in layers of fruit, capable of withstanding severe changes in climate. Flowering plants have also provided us with a great variety of fabulous fruit, vegetables and cereals, which we eat everyday. Until Australia separated 45 million years ago it's plants and animals were identical to that of its neighbours. As the sea widened between Australia and Antarctica, Australia began to drift north, it became like a boat with living cargo. While some plants continued to grow and remained almost unchanged from then till now, others became adapted to new and changing environmental conditions. Australian life forms evolved in their own way, as they were totally isolated from what was happening in other continents. Australia also began to develop its own unique forms of plant and animal life. For at least 30 million years Australia remained too far away from any other landmass to be colonised by plans and animals from outside places. As it came closer to Asia in more recent times, some new plants invaded the continent from there. We can think of Australia having its biosphere made up of 3 parts. Firstly there are Ancient plants dating from before the continents separated (these plants are therefore shared by other continents). These plants which fit into this era are mostly to be found in rainforests. Before Australia separated, rainforest vegetation was widely spread across it. It contained the ancient conifers and early primitive flowering plants. As Australia moved away from the equator, it became drier and rainforests areas shrank in size. After that came the unique Australian plant life, which evolved here in isolation. The new vegetation had to adapt not only to drier conditions but also poorer soils. The new vegetation had to be very different, but gradually the eucalypts (gum trees), the acacias, spinifex and many other plants that made up the Australian landscape came into being. In the final step came the new immigrant plant life from Asia. As Australia came into closer contact with Asia about four million years ago, some of Asia's plants began colonising suitable parts of Australia. As they were not adapted to dry conditions, the only suitable conditions for them were wet coastal areas of the north and parts of the tropical rainforest of Queensland. These immigrants included many new species of palms, paperback trees, ferns, vines, and mangroves. So over the millions of years the earth has been evolving, so have the plant species that we now live among.