Transcript Early Life
Earth History GEOL 2110 Early Life Chapter 9 Major Concepts • The oldest fossils known are filaments of cyanobacteria (blue-green algae) that are 3.5 billions years old • Experiments simulating the origins of life are able to create the building blocks of life (proteins and amino acids) from the primordial soup of the early earth oceans and oxygen-depleted atmosphere. • Simple, asexually reproducing, single-celled organisms persisted until 700 million years ago. • The first multicellular organism appeared as soft-bodied creatures around 700 million years ago during a period of extensive global glaciation, supercontinent breakup, and carbon infusion into the oceans • The appearance of organisms with skeletons appeared in the Cambrian after a significant increase in oxygen •Conditions on Earth 3.5-4.0 Ga Oxygen deficient (anaerobic) atmosphere Late Heavy Bombardment (4.1-3.8 Ga) Oceans present since 4.2 Ga (very warm) Darwin’s “Warm Little Pond” - Primordial Soup (CH4, NH3, CO2, N2 rich) – all the components necessary to make life Intense UV bombardment (no ozone) Origin of Life: Early Ideas • Spontaneous Generation – process of putrefaction somehow producing metamorphosis of nonliving to living matter • Louis Pasteur's sealed flask If life doesn't spontaneously generate experiments now, how could it in the past? Recreating the “Warm Little Pond” Miller demonstrated that a wide range of vital organic compounds (amino acids, cyanide, formaldehyde) can be synthesized by fairly simple chemical processes from inorganic substances Stanley Miller 1930- 2007 Making Polymers Sidney Fox 1912-1998 Polymer – complex chains of linked simple organic molecules (proteins, nucleic acids, sugars, fats, enzymes) Experimentally derived in a number of ways – splashing amino acids under hot, dry conditions forming proteins (Sidney Fox) – Cyanide, clays, and heat capable of polymerizing amino acids into proteins - Can form nucleotides under similar conditions (heating of ammonium and cyanide – Miller) Protenoids behave much like bacteria, regulate their cells, excrete waste, metabolize sugars Cell membranes Formed from fatty acids carboxyl group (COOH) and aliphatic chain Fatty acid (hydrophobic) + alcohol (hydrophyllic) form lipids Lipids form cell membranes that regulate what goes in an out of a cell Actually easy to synthesize as well as found on meteorites Reproduction Coding and Replication Which came first? Protein synthesis or nucleic acid (RNA) Current thinking is RNA evolved first as “naked genes” and become encoded with the help of ribozymes Other Templates suggested for serving as templates for reproduction are: Clays, Zeolites, and Pyrite (FeS2) Single-celled Prokaryotes Rule 3,500 – 700 Ma 3.5 Ga Cyanobacteria Australia 1.15 Ga 4-celled cyanobacteria in chert Modern filamentous cyanobacteria, Lyngbya 3.4 Ga stromatolite Swaziland Supergroup, South Africa Evolution of Prokaryotes and Eukaryotes Reducing, sulfur-rich Hydrothermal vents Photosynthesizing bacteria Fig. 9.7 Prokaryotes and Eukaryotes Evolution of Eukaryotes More complex eukaryotes are thought to have developed from symbiotic relationships between prokaryotes Symbiotic origin of Eukaryotes around 1.75 Ga, didn't diversify much until 1.1 Ga (sexual reproduction?) Multicellullar Organism (Metazoans) Appear ~ 600Ma Ediacaran Metazoan Trace Fossils Metazoan fossils from Ediacara Hills, Australia, 600 to 550 million years ago. Soft bodied - like jelly fish or sea pens Cambrian Explosion (535--510 ma) • Soft bodied organisms replaced with many fossils of shelled invertebrates • Significant amounts of burrowing/trace fossils • Large diversification of fossil record • Likely related to the end of the extreme Varangian glaciation and increased tectonic rifting of Rodinia Additional contributors to the Cambrian Explosion Potentially higher atmospheric O2 (close to modern concentrations) promotes calcite exoskeleton secretion (phosphate and silica common under low O2 conditions). Increased nutrients associated with more rifting and volcanic activity Abundant cyanobacterial mats for molluscs and other small invertebrates to graze Development of predators Tiering of biotic activity on the sea floors Burgess Shale Middle Cambrian from Field, British Columbia (discovered in 1909) Abundant well preserved fossils of soft bodied animals Highly experimental forms Summary of Early Earth Events Next Lecture Vendian, Cambrian and Early Ordovician Periods Part I Chapter 10