Although millions of species have become extinct over the course of life's history, some species have always survived. Echoes of these species can still be found, even when one looks at a nearby lake.

The very first organisms were prokaryotic bacteria and archaea. As prokaryotic organisms, they consisted of only one cell which had no nucleus or specialized organelles. More complex cell structures emerged as bacteria and archaea cells were combined. For example, the chloroplasts of plant cells were originally photosynthetic bacteria that began to live inside other cells. Protists were primitive unicellular organisms. They are not fungi, animals, or plants.
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The traditional categorization of living organisms.

Cyanobacteria are among the oldest organisms one can see when studying a lake. These photosynthetic bacteria emerged over 3,5 billion years ago. They were among the first organisms that could produce energy from sunlight using photosynthesis. As a result of photosynthesis, oxygen was gradually introduced into the atmosphere.


Cyanobacteria are photosynthetic bacteria. 

Our lakes are home to a large variety of microscopically small unicellular algae and protists. Their cells are more developed than those of bacteria, as they have nuclei and organelles. All multicellular organisms, such as plants and animals, have descended from these kinds of organisms.

Plants moved to land before animals could. The oldest fossils of land plants date back to over 400 million years ago. They were a type of moss that would grow in shallow shore water. Plants diversified and grew in size drastically during the Carboniferous period. During this time, the lake shores of Finland were dominated by large fern forest.

Most species that inhabit our lakes are invertebrates. Many groups of invertebrates are quite old. For example, zooplankton such as water fleas have existed over 600 million years ago. 

Flying insects developed during the same time as land plants grew more common. Dragonflies are among the oldest insect groups one can see in a lake. They developed 300 million years ago.

Fish are the earliest group of vertebrates. Most fish that can be found in Finnish lakes belong to the group of bony fish. Their fossils have been dated back over 450 million years. 

Amphibians were the first vertebrates to move to the land some 400 million years ago. However, although they could live on the land, their reproduction was still dependent on water environments. Reptiles were the first vertebrates that could reproduce on dry land. 

Angiosperm or flowering plants are a relatively new group of plants that emerged under 65 million years ago. Most of the plants you see on the lake shore are angiosperms. During the same time as angiosperms developed, the animal kingdom diversified through birds and mammals.