"Origin of Life on Earth"
Georgia Tech School of Biology Origin of Life on Earth • Spontaneous generation – Greek philosophers to 19th Century Europe • Steps in the origin of life • Critical role of RNA • Evolutionary milestones • Three domains of life Biology 1510/1511 Fall 2008 Georgia Tech School of Biology Spontaneous Generation – Early Views • Anaximander (ca. 611-547 BCE) – Living creatures form in water when acted on by sunlight. – The original living organisms differed from those now extant, and humans originated from some kind of fish. • Anaximenes (588-524 BCE) – The sun’s action on a primordial terrestrial slime made of earth and water led to the formation of plants and animals Anaximander image: http://www.mlahanas.de/Greeks/Bios/Anaximander.html Biology 1510/1511 Anaximenes image: http://en.wikipedia.org/wiki/Image:Anaximenes.jpg Fall 2008 Georgia Tech School of Biology Spontaneous Generation – Aristotle • Aristotle (384-322 BCE) was the most prominent Greek naturalist. – Four terrestrial elements: earth, air, fire, water – Organisms derive their properties from the four elements and a vital force (“pneuma”). – Described various types of spontaneous generation: • Insects generated from dew falling on leaves • Bivalves form spontaneously in mud or sand • Some fish form like bivalves (i.e., from mud or sand) Biology 1510/1511 Image: http://www.philosophypages.com/ph/aris.htm Fall 2008 Georgia Tech School of Biology Spontaneous Generation – 19th Century • Lamarck (1724 - 1829) – Each species arose from an independent event of spontaneous generation. – Spontaneous generation continues today. • Pasteur (1822 - 1895) – Demonstrated experimentally that microbes would not appear in flasks protected from dust and other small particles. – Spontaneous generation does not happen today on experimental time scales. Lamarck image: http://bio.research.ucsc.edu/people/bernardi/Marina/public_html/Bio175/Bio175Website/Index.html Biology 1510/1511 Pasteur image: http://www.uab.edu/reynolds/MajMedFigs/Pasteur.htm Fall 2008 Georgia Tech School of Biology Steps in the Origin of Life • Formation of organic molecules – Can occur spontaneously. • Polymerization to form macromolecules – Minerals may have acted as a template • Protobiont formation – Can form spontaneously under laboratory conditions. • Development of a hereditary mechanism – RNA as both enzyme and genetic material. Biology 1510/1511 Fall 2008 Georgia Tech School of Biology Earth 3 Billion Years Ago Biology 1510/1511 Campbell & Reece 7th Edition, Fig. 26.01 Fall 2008 Georgia Tech School of Biology Miller & Urey Experiment • Simulated early earth with a strongly reducing atmosphere, an ocean, and a hydrologic cycle. – Energy inputs via heating & an electrical discharge. – Inorganic reactants CH4, NH3, and H2 • Amino acids and other organic molecules formed spontaneously under these conditions. • The building blocks of living organisms can form spontaneously on short time scales. Biology 1510/1511 Campbell & Reece 7th Edition, Fig. 26.02 Fall 2008 Georgia Tech School of Biology What of a Less Reducing Atmosphere? • Simple organic molecules are much harder to generate in a less reducing atmosphere. – Marine environments out of direct contact with the atmosphere may have provided a critical site for organic material synthesis. – Hydrothermal vents are an excellent environment for synthesis of organic molecules. – Genomic studies imply a high- temperature origin of life. Biology 1510/1511 Campbell & Reece, Fig. 25.02 Fall 2008 Georgia Tech School of Biology Protobionts • Liposomes – Membrane-bound droplets – Form spontaneously from lipids and organic molecules in aqueous solution. – Primitive “metabolism” may occur when molecules with enzymatic activity are included in the mix. Biology 1510/1511 Campbell & Reece, Fig. 25.03 Fall 2008 Georgia Tech School of Biology RNA and DNA • Genetic information is now encoded by DNA, but DNA synthesis requires proteins, and proteins in turn are encoded by DNA… • In contrast to DNA, RNA can show enzymatic activity as well as encode genetic information. – Ribonucleotides are more easily formed than deoxyribonucleotides – Ribozymes are capable of self- splicing and copying Biology 1510/1511 Campbell & Reece, 7th Edition, Fig. 26.05 Fall 2008 Georgia Tech School of Biology Microfossils Bitter Springs Chert, 850 Maa Gunflint Chert, ca. 2 Ga Biology 1510/1511 Campbell & Reece, Fig. 25.04 Supplementary Images Fall 2008 Georgia Tech School of Biology Three Domains of Life 4 Symbiosis of chloroplast ancestor with • All organisms we know of ancestor of green plants on Earth today are descended from a common 3 Symbiosis of mitochondrial ancestor that lived about 4 ancestor with ancestor of billion years ago. eukaryotes 2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells 1 Last common ancestor of all living things (LUCA) Campbell & Reece 7th Edition, Fig. 25.18 Campbell & Reece, Fig. 26.21 Biology 1510/1511 Fall 2008 Georgia Tech School of Biology Evolutionary Milestones • Life arose from nonlife • The first organisms were single cells • Speciation has generated the diversity of life • Eukaryotes are "cells within cells" • Photosynthesis and sex changed the course of evolution - and the planet • Multicellular organisms developed relatively late in Earth history. Biology 1510/1511 Fall 2008