Oldest confirmed evidence of microbial life
is around 3.5 billion years from the beginning, putting the start of life between 4 - 3.5
billion years -- soon after water condensed.
Eukaryotes appeared around 2 billion
years ago and multicellular life around 1 billion. Vertebrates at 400
million years, mammals at 240 and humans only 2 million years ago.
The Temperature of Life
The world around us is inhabited by mesophiles: organisms adapted to live around the same temperature range as we do. Organisms that can live above about 50 °C are called thermophiles.
Three Great Domains
All cellular life on earth can be classified as belonging to one of three domains:
The first, Eukarya, includes humans and all organisms with a nucleus. Bacteria and archaea are unicellular prokaryotes (lacking a nucleus). They have many features in common, but are now generally recognized as constituting two fundamentally different domains of life.
LUCA (the Last Universal Cellular Ancestor) is the progenitor cell from which all life has evolved (a sort of microbial Eve).
There is a lot of debate about what LUCA was.
We can be pretty certain that it was already a complex life form with hundreds of genes encoded by a DNA or RNA genome, a cell membrane and a protein complement for metabolism and information processing.
This tree is drawn to reflect the theory that the archaea and eukarya are more closely related to one another than either is to the bacteria (compare the last common ancestors denoted by the blue and red arrows).
This still controversial theory arises from the analysis of genome sequencing projects over the last eight years, which shed light on the unexpected relationships between eukarya and archaea in the ways in which they process information (in other words DNA replication, transcription and translation).
The archaea are split into two deep subdomains: euryarchaea and crenarchaea. The former includes the methanogens and halophiles, whilst the crenarchaea are some of the most hyperthermophilic organisms known, growing at up to 113°C.
Many archaea however are not extremophiles, and are found in temperate seawater and soil. It is now believed that archaea constitute a significant proportion of the biosphere.
Archaea are found in many harsh environments on the planet, and have adapted to live at extremes of temperature (from Polar ice to superheated water), pressure, pH ( from extreme acid pH 0 to alkaline pH 10) and salinity (saturated NaCl in salt pans and the Dead Sea).
Archaea constitute a major portion of the biosphere, and are also present in soil, temperate sea water and even the human gut. To survive in extreme environments like boiling acid, every component of the cell must be adapted: for example proteins must be stable and functional at temperatures where "normal" proteins fall apart.
Recently, a privately held research firm, ArchaeaSolutions, Inc. has been able to develop commercial applications for archaea's use in decomposition of organic matter in wastewater treatment plants. Learn more about how ArchaeaSolutions, Inc., can reduce disposable biosolids, ammonia, nitrates and odor in wastewater.