Astrobiology

Studying the Earth history revealed that life appeared on our planet after its surface had adequately cooled down, around 3.8 billion years ago. Fossil evidence indicated that the first organisms were unicellular (one-celled) and anaerobic (non-oxygen requiring). By studying extreme environments such as thermal vents, the freezing waters of the Antarctic, and anoxic marine sediments, scientists are able to determine mechanisms of microbial evolution, and reconstruct the early history of life on Earth.

The evolution of life on Earth is closely linked to extraterrestial intervention in form of asteroids, comets NASA's Mars Viking Lander (full-scale operational model) its arm extended as it would be to collect a soil sample to be examined for chemical indicators of biogenic activity. © Lowell Georgia/Corbis. Reproduced by permission.

and meteors. These objects falling onto Earth were likely to bring inorganic and organic compounds used later to create proteins and DNA, the basis of life, as it is known today. Analysis of space dust from our galaxy and beyond revealed presence of ammonia and organic compounds such as glycine, vinyl alcohol, benzene, polycyclic aromatic hydrocarbons, and formaldehyde.

The crushing of large objects onto the Earth's surface not only brought new molecules to Earth, but also often had catastrophic consequences leading to sudden climate changes and mass extinctions (for example, the disappearance of the dinosaurs). Events from Earth's past were described by scientists studying fossils, rocks, and more recently, Greenland's and Antarctic ice sheets.

Signs of life on planets and moons of the solar system are investigated by analyzing meteors that landed on Earth. These, however, could have been potentially contaminated by terrestrial material making it impossible to interpret the results. Therefore, the studies of rocks originating on Mars are much more interesting, provided that samples are kept in isolation. Clues to the existence of extraterrestial life are also provided by studies of the chemistry and geology of the surface of planets and moons. The presence of hydrated salts and formations similar to ice fields of the Antarctic were identified on Jupiter's moons Callisto, Europa, and Ganymeda.

Beside searching for life in and beyond our solar system, astrobiology is involved in studying the response of Earth lifeforms to weightlessness in orbit and possible space travel. Space shuttle missions have investigated the effects of lack of gravity on the physiology of human and animal bodies and their immune system, plant growth in space, and fertilization. Early twenty-first century planned research includes flying worms into space and studying gene expression in their multiple generations to see if weightlessness affects them similarly to vertebrates. So far, the main problems encountered with prolonged stay in space are muscle atrophy (shrinkage), loss of bone mass, and radiation exposure, especially during walks outside the shuttle.