Early Earth and The Origin of Life Chapter 20

The Origin and Evolution of Life Chapter 20

The Big Bang billion years ago all matter was compressed into a space the size of our sun Sudden instantaneous distribution of matter and energy throughout the known universe

Earth Forms 4,600 mya: Origin of Earth 4, ,800 mya –Formation of Earth’s crust, atmosphere –Chemical and molecular evolution –First cells (anaerobic bacteria)

Earth Forms About 4.6 and 4.5 billion years ago Minerals and ice orbiting the sun started clumping together Heavy metals moved to Earth’s interior, lighter ones floated to surface Produced outer crust and inner mantle

Earth Is “Just Right” for Life Smaller in diameter, gravity would not be great enough to hold onto atmosphere Closer to sun, water would have evaporated Farther from sun, water would have been locked up as ice

First Atmosphere Hydrogen gas Nitrogen Carbon monoxide Carbon dioxide No gaseous oxygen

Origin of Organic Compounds Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth Clay may have served as template for complex compounds Compounds may have formed near hydrothermal vents Oparin hypothesized that energy from lightning could have caused organic molecules to form from inorganic compounds in Earth’s primitive atmosphere.

Miller-Urey Experiment In 1953, Miller and Urey did an experiment that simulated lab conditions that were similar to those of the early Earth After one week, they found a variety of organic compounds (including amino acids) that had been produced from inorganic material

Miller-Urey Experiment

Chemical Evolution Spontaneous formation of porphyrin rings from formaldehyde Components of chlorophylls and cytochromes formaldehyde porphyrin ring system chlorophyll a Figure 20.4 Page 720

RNA World DNA is genetic material now DNA-to-RNA-to-protein system is complicated RNA may have been first genetic material RNA can assemble spontaneously and can carry out enzyme-like catalytic functions. (These enzyme-like, self-replicating pieces of RNA are known as ribozymes.) How switch from RNA to DNA might have occurred is not known. Ribozymes might have somehow served as a template for DNA production.

Proto-Cells Microscopic spheres of proteins or lipids can self assemble Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools

Protobionts Collections of abiotically produced molecules surrounded by a membrane Exhibit simple reproduction and metabolism. Small membrane bound droplets called liposomes can form when lipids are added to water.

Possible Sequence membrane-bound proto-cells living cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNARNA enzymes and other proteins formation of protein-RNA systems, evolution of DNA formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Figure 20.5 Page 331

Proterozoic Eon Origin of photosynthetic Eubacteria –Noncyclic pathway first –Cyclic pathway next Oxygen accumulates in atmosphere Origin of aerobic respiration

The First Cells Originated in Archeon Eon Were prokaryotic heterotrophs Secured energy through anaerobic pathways –No oxygen present –Relied on glycolysis and fermentation

History of Life 3.8 bya3.2 bya2.5 bya ORIGIN OF PROKARYOTES ARCHAEBACTERIAL LINEAGE ANCESTORS OF EUKARYOTES Cyclic pathway of photosynthesis Noncyclic pathway of photosynthesis Aerobic respiration Figure 20.6 Page 332

History of Life ORIGINS OF EUKARYOTES ORIGINS OF MITOCHONDRIA ORIGINS OF CHLOROPLASTS 1.2 bya900 mya435 myapresent ORIGINS OF ANIMALS ORIGINS OF FUNGI ORIGINS OF PLANTS ARCHAEBACTERIA Extreme halophiles Methanogens Extreme thermophiles EUKARYOTES Animals Heterotrophic protistans Fungi Photosynthetic protistans Plants EUBACTERIA Figure 20.6 Page 332 Photosynthetic oxygen producers Other photosynthetic bacteria Chemotrophs, heterotrophs

Advantages of Organelles Nuclear envelope may have helped to protect genes from competition with foreign DNA ER channels may have protected vital proteins DNA infolding of plasma membrane Figure Page 335

Theory of Endosymbiosis Lynn Margulis Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts

Timeline of Life on Earth

Kingdoms of Life Arranging the diversity of life into kingdoms is a work in progress There are multiple ways to categorize the forms of life Some diagrams to be familiar with…

Kingdoms of Life Most do not use this 5 kingdom system today! Kingdom Monera has been divided into two kingdoms.

Kingdoms of Life

Classification Levels Domain Kingdom Phylum/Division (for plants & fungi) Class Order Family Genus Species

Classification Scheme Based on work of Carolus Linnaeus Father of taxonomy Father of binomial nomenclature Genus species Genus is a noun that describes the organism. Species name is an adjective describing it. Genus (capitalized & underlined) species (never capitalized & underlined)