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Life on Earth II
Life on Earth Part 2

Professor Philip Hugenholtz, ARC Australian Laureate Fellow and Director of the Australian Centre for Ecogenomics at the University of Queensland, places the tree of life under the microscope with the focus on a key feature: microorganisms The first life on Earth was single celled, thought to be the forerunner of the domains of bacteria, archaea and eucarya. Our first physical records of life are of microbial mats which are evidence of huge communities of microbes aggregated together for common good (eg survival by not being buried by layers of sediment) Groups of microorganisms gradually formed extensive thick mats or built up stromatolites (mound shaped objects), some structures surviving over 3.5 billion years - quite an achievement for what was basically a biofilm produced by a microscopic single celled organism. A famous example that stretches for hundreds of kilometres in the ocean off Guerrero Negro, Mexico is 20cm thick. Microorganisms are hardier than people think, mould or scum being a case in point. Different species thrive in temperatures from sub-freezing to above boiling point and can survive without any oxygen or in super-oxygenated environments. They can even survive in radioactive bioreactors. Microorganisms work as a team, sharing nutrients and taking up different functional parts of the food web. There are many advantages in living together as a community, protection being one. While we lack physical fossil records of the evolution of both diverse singled celled and later multicellular organisms, advances in genetic research have made it possible for scientists to look for genes common to all forms of life, and so building up a tree of life to show this evolutionary history. In terms of survival, climate change is a case in point. The Earth has seen many big changes, there always being winners and losers, organisms that can’t adapt dying out. In this regard microorganisms are in a much safer position under climate change than humans who are less adaptive in terms of physiology while many microorganisms will easily adapt to such changing circumstances.

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