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The oldest known fossils on Earth are stromatolites, which were formed by cyanobacteria about 3.5 billion years ago and can still be found on Earth today.
Image at right: living stromatolites, a stromatolite section sliced to reveal layers, and cyanobacteria responsible for the formation of stromatolites.
Scientists expect that if life evolved on Mars it is most likely to be bacteria or simple organisms. Could cyanobacteria survive in the harsh martian conditions?
Extremophiles
Extremophiles
On Earth, organisms that live in extreme environments are known as extremophiles, and they thrive in environments that can be extremely salty, acidic, and/or hot and freezing cold. They live in places like the hot, acidic mineral springs in Yellowstone National park; near hydrothermal vents deep beneath the oceans; in the soil of dry deserts blasted by solar radiation, and beneath the ice in antarctic lakes.
Extremophiles might be tough enough to survive in the harsh martian environment. The most likely place to look for evidence of extremophiles is where there is evidence of water. Even if life no longer exists on Mars, there may be fossilised evidence that it once did.
Microfossils
Microfossils
Microfossils are extremely small and require a microscope to view them effectively. Microfossils are normally collected in the field and taken back to the laboratory for examination under the microscope. See image below. The 'rock' when examined under the microscope reveals broken fragments of diatoms, a common type of phytoplankton. The next two images are of microfossils viewed under a microscope.
TASK: Where would you expect to find evidence of past or present life on Mars? Explain your reasoning.
The record of past environments is preserved in the landscape, and we can unlock the story of what Mars was like in the past by studying the geology.
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