Twylo spent several million years forming. During this time its iron core was converting from liquid to solid, with the heavier materials settling in the core. Hot gasses escaped through volcanic eruptions and cracks in Twylo's crust. Twylo was uninhabitable during this period; the temperature was too hot and toxic gases continually seeped into its atmosphere.
About 500 million years ago, Twylo began to cool and reach the more temperate climate of today. Twylo's oceans were rich in minerals from the millions of years of volcanic activity. Here, deep in the oceans, Twylo's first life forms emerged. These unicellular organisms thrived on the radiation found in the deposited lava rocks. Many of these organisms died off rapidly, hardly leaving traces of their existence. Although traces of these organisms are still found in parts of Twylo's oceans, they are most concentrated near the warmer areas of the equator.
This computer-generated drawing shows one of Twylo's first unicellular organisms, the Unidom. The Unidom is "reinventing" itself, a unique mechanism for adaptation and survival.
The Unidom uniquely adapted to its precarious ocean surroundings by developing a hard cell wall. Also, in times of stress, such as harsh temperature changes, the Unidom can "reinvent" itself. Similar to cell division, this reinvention process allows the Unidom to change slightly to adjust to its new environment. Although the changes are subtle, they occur so rapidly that sufficient changes can occur in a short period of time. These changes allow the Unidom to withstand the new environmental challenge. In the picture of the Unidom above, the reinventing process is taking place. The Unidom's nucleus, as depicted by the black spot with tentacles, is escaping to reform itself. It's DNA will change slightly as the Unidom reinvents itself.
About one million years after the first Unidoms and similar organisms appeared, the Chlordoms emerged. Twylo experienced a period of intense tornadoes and hurricanes during this period. The oceans churned and many of the unicellular organisms were thrust to the ocean surface. Some seemed to swim about like animals. Others floated in the water and resettled on the ocean floor. The surviving surface organisms began to cling to each other for survival. The crashing waves annihilated many of these one-celled organisms but eventually large colonies of survivors emerged. In the new surface environment these one-celled survivors found a new energy source--sunlight. Their next challenge was to mutate in order to utilize this new energy source.
The cell wall was one of the first changes which occurred. The previous hard cell wall transformed to a slimy, jellylike cell covering. This new covering protected the organisms from losing water and from unfavorable conditions. The second major change these organism underwent was the inclusion of chlorophyll in their cells. With the inclusion of chlorophyll, the organisms were able to make their own food through photosynthesis. With the inclusion of chlorophyll these organisms thrived and experienced a population explosion. The shapes of these next generation organisms, known as Chlordoms, were very varied. They had to stay near the surface, to get light. But their jelly-like cell walls were dense and they had to counteract the tendency to sink. They stayed near the surface partly by storing energy as oil, which gave them buoyancy, and partly by becoming long and skinny, which slowed their settling. The specimen whose end is shown below is only about 6 microns wide, but the cell is about 80 microns long; it is stretched very thin.
This picture shows an early Chlordom with its slimy cell wall, elongated shape, and its green chlorophyll.
The Unidoms and Chlordoms were both unicellular organisms. Although the Clordoms prospered in colonies, each lived independently and did not have to depend on any other to survive. They reproduced primarily through cell fission. Later forms of the early Unidoms and Chloridoms also reproduced through producing spores. These spores could immediately swim about or remain quiet for weeks or months until the conditions were right. These spores then formed new Chlordom-like organisms.
Two million years after the
Chlordoms appeared, Twylo's weather conditions calmed and the
Chlordoms and other unicellular organisms thrived. These conditions
allowed new organisms to evolve. Many of the Chlordoms, which
were already living in large colonies, began to attach to each
other during cell division. DNA from neighboring Chlordoms dividing
at the same time became incorporated into a new Chlordom. The
Unicellular Chlordoms gave rise to Twylo's first aquatic plants.
These multicellular plants are discussed in the next chapter.
This drawing shows the evolution of the unicellular Unidoms and Chlordoms to the multicellular plants discussed in the next chapter.