Mars and Early Life on Earth

The Mars rock was discovered on the Allan Hills ice field in Antarctica in 1984. The composition of the gas trapped in the rock is a close match to known Martian atmosphere and shows that the rock came from Mars. The rock is approximately 4.5 billion years old and there is evidence that water seeped into the rock ca. 3.6 billion years ago. The rock remained buried on Mars until 16 million years ago when an asteroid striking Mars' surface blaster it into space. It fell to earth 13,000 years ago.

SEM of beasties, carbonate and magnetite crystals normally associated with life on earth. The size of the rod- and spherically-shaped objects are similar in size to archaean bacteria.

Comparison of a Eubacteria cell (E. coli) with Archaebacteria.

Black smokers support a variety of archaea. The discovery of the archaea in extreme environments suggests that life evolved under hellish conditions.

Other organisms feed on the archaea.

Other examples of Archaean habitats.

Geologic time is divided into the following time frames:

• The Cambrian (Phanerozoic) Eon represents the time during which the first complex life forms arose (the Cambrian Explosion). During the Precambrian Eon it was once thought that only simple, one-celled organisms (or loose colonial forms) existed. We now know that the first animal life arose before the Cambrian during the Vendian period (650-540 mybp). These first animal forms are known as the Vendian animals or Ediacarans.
• During the Hadian era life was probably not possible because of extreme temperatures an massive bombardment by asteroids and comets. One Mars-sized chunk of rock hit the Earth during this era and is responsible for the formation of the moon (look here).
• By the Archean era we start seeing the first evidence of life starting with chemical fossils, followed by microfossils of cyanobacteria (including stromatolytes). The first of the bacterial forms were in the archaea domain and probably came to life near volcanic vents (see the Archaean era here). The cyanobacteria were responsible for changing the atmosphere from a reducing to oxidizing.
• The Proterozoic era is characterized by the first eukaryotes (probably an adaptation to increasing oxygen levels. During this time the ediacarans evolved.

Louis Pasteur was responsible for ground-breaking research in medicine and chemistry, including germ-theory, immunization, and, of importance here, research on fermentation and spontaneous generation (more on Louie is here). Before this research even educated people believed that complex life forms arose spontaneously from non-living objects. Horse hair worms (nematomorphs) sprung from horse manes that had fallen into a watering trough and rats or mice developed directly from the grain in open bags in a barn. A flask of the type used to disprove spontaneous generation is depicted at the upper right. Broth was boiled in two flasks (Pasteurization). The trap of one flask was sealed to ensure that germs in the air could not gain entrance while the second flask remained open. After several weeks the open flask became cloudy with bacteria while the sealed flask remained clear, proving that spontaneous generation did not take place.

Present evolutionary biologists suggest that simple life forms were spontaneously generated about 3800 mybp (Abiogenisis) or arrived from space (Panspermia). In either case, there still would be a spontaneous generation of life (panspermia only pushes the event off-world). The explanation is that today's conditions are very different from those that existed during the Archean era. An oxygen atmosphere would destroy many of the biotic compounds that might spontaneously form today. Others would be gobbled up by existing creatures and, if any primitive life forms were to spontaneously evolve, they would not be able to compete with more advanced life forms.

The flowchart depicts the major requirements for the abiogenisis of life. Most has been understood for 30 - 40 years. Major changes are related to the realization that thermophylic chemosynthetic archaea (or something like them) represent the most likely first life form. Understanding that life arose in an environment that we would today call extreme has provided clues as to how pathways, self-assembly and other thorny problems might have occurred.

In 1924 Operon hypothesized that the early earth was enveloped in a reducing atmosphere (methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water (H₂O)). Energy from lightning and other sources reacted to form an organic ooze Haldane called the primordial soup.

The Miller-Urey spark gap apparatus. Simulated lightning was passed through a reducing atmosphere to form amino acids and other organic building blocks. Other than the reducing atmosphere, conditions for the evolution of early life was thought to be similar to today's (the Garden of Eden theory). Stanley Miller simulation is here!

Vents and relation to 3 domains

Major events that may have occurred at hydrothermal vents. Initially, the first cells are thought to have been a component of the geothermal system (i.e., actually part of the rock without cell membranes). The first pathways developed in these "organisms". As the geothermal-coupled protocells differentiated into free, individual cells the first of the archaea evolved (probably iron sulfide metabolizing thermophiles). This seed later serves as the progenitors of the eubacteria (true bacteria) and eucarya (eucaryotic cells)

Natural and artificial pyrite membranes that can form at hydrothermal vents. These structures provide both a method of compartmentalization and a conductive layer for electron transport.

Metal membranes based on the conductive properties of the FeS membranes are found in a primitive archaeon (Methanothermus farvidus). Structures such as these in a living archaeon supports the assumption that metal membranes served as the initial cell compartmentalization mechanism while simultaneously providing a transport mechanism to power a primitive protometabolism.

Amino acids can also be generated at the vent by relying on reactions that have been observed in the Miller spark-gap experiment.

Stromatolites. More on Stromatolites is here. Jump to Microfossils

Another time line

Cassini-Huygens Mission A quickie on the Cassini-Huygens mission is here.