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The chemical reactions that preceded living organisms probably occurred in specialized compartments, such as water droplets on the surfaces of minerals. Life as we know it did not begin until the emergence of cells. Protocells made in the laboratory have some of the properties of modern cells. Cell-
learning outcomes
You should be able to:
Justify the reasoning behind the hypothesis that a membrane was critical in the evolution of life on Earth.
Describe the evidence suggesting that microfossils may be the remains of early cells.
Why is the cell membrane important to the evolution of living organisms?
The cell membrane forms a compartment in which the chemicals needed for the reactions of life can be concentrated. The membrane creates a suitable internal chemical environment for the organism that is distinct from that of the environment.
If you wanted to find evidence for the existence of cells more than 3 billion years ago, what would you look for?
First, examine rocks that are more than 3 billion years old. Then look at slices of rocks under microscopes for objects that look like cells or chains of cells. Finally, chemically analyze the rocks for chemical signatures for life, such as a carbon isotope ratio resulting from photosynthesis.