AP Biology, Chapter 26
Early Earth and the Origin of Life

Summary
Introduction
	1. Explain how the histories of Earth and life are inseparable.
		a. Geological events affect biological evolution
		b. Organisms cause major chemical changes on Earth

INTRODUCTION TO THE HISTORY OF LIFE
	Introduction
	Life on Earth originated between 3.5 and 4.0 billion years ago
	Major episodes in the history of life
		2. Describe the major events in Earth's history from its origin up to about 2 billion years 
		ago. In particular, note when Earth first formed, when life first evolved, and what forms 
		of life existed up until about 2 billion years ago.
			a. 4.5 bya Earth forms
				.Atmosphere from outgassing by volcanoes
				.H2, NH3, CH4, NOX, and CO2
				.= a reducing atmosphere
			b. 3.5-4 bya cellular life appears
			c. 3.5 bya oldest fossils (stromatolites)
			d. 2-3 bya Archaea and Bacteria diverge
			e. 2.5-2.7 bya oxygen gas appears in large amounts
			f. 1.7 bya oldest fossils of eukaryotes
		3. Describe the timing and significance of the evolution of photosynthesis.
			a. 3.5 bya (?) non-oxygenic photosynthesis
			b. 2.7 bya oxygenic photosynthesis 
			c. 2.2 bya significant accumulation of atmospheric oxygen 
		4. Describe the timing of key events in the evolution of the first eukaryotes and later 
		multicellular eukaryotes. Describe the snowball-Earth hypothesis.
			a. Events
				i. 2.1 bya oldest definite eukaryote fossils
				ii. 2.7 bya origin based on chemical traces; endosymbiosis
				iii. 1.5 bya multicellular eukaryotes
			b. Snow-ball Earth: completely frozen 750-570 mya
		5. Describe the timing of key evolutionary adaptations as life colonized land.
			a. 1 bya microscopic terrestrial life
			b. 500 mya macroscopic terrestrial; waterproofing tissues

PREBIOTIC CHEMICAL EVOLUTION AND THE ORIGIN OF LIFE
	Introduction
	The first cells may have originated by chemical evolution on a young Earth: an 
	Overview
		6. Contrast the concept of spontaneous generation and the principle of biogenesis. 
		Describe the biogenesis paradox and suggest a solution.
			a. Spontaneous generation: former belief that life can emerge from non-living
			b. Biogenesis: life by reproduction from pre-existing life
			c. Paradox
				i. Where did the first living things come from?
				ii. Solution: early Earth was different, very long periods of time were 
				involved
		7. Describe the four stages of the hypothesis for the origin of life on Earth.
			a. Abiotic synthesis of small organic molecules
			b. Polymerization
			c. Self-replication molecules
			d. Packaging into membraneous protobionts
			
	Abiotic synthesis of organic monomers is a testable hypothesis: science as a process
		8. Describe the contributions that A. I. Oparin, J. B. S. Haldane, and Stanley Miller made 
		toward developing a model for the abiotic synthesis of organic molecules. Describe the 
		conditions and locations where most of these early organic reactions probably occurred 
		on Earth.
			a. Contributors
				i. Oparin and Haldane: conditions on the early Earth favored the 
				formation of small organic molecules
				ii. Miller simulated conditions on the early Earth
					.Water for oceans
					.H2, NH3, and CH4 for atmosphere
					.Sparks for lightning
					.Formed amino acids
			b. Submerged volcanoes and deep-sea vents have the chemicals and energy
	Laboratory simulations of early Earth conditions have produced organic polymers
	Protobionts can form by self-assembly
		9. Describe the key properties of protobionts in the evolution of the first cells.
			a. Protobionts are aggregates of abiotically produced molecules
			b. Properties
				i. If enzymes are included they metabolize
				ii. Selective permeability
				iii. Discharging membrane potential = excitability
				iv. Can absorb and split into smaller units
				v. Lack hereditary traits 
	RNA was probably the first genetic material
		10. Describe the evidence that suggests that RNA was the first genetic material. Explain 
		the significance of the discovery of ribozymes.
			a. RNA is central to information transfer in cells
			b. RNA can be copied abiotically
			c. Ribozymes have a variety of catalytic functions; pre-date enzymes
		11. Describe how natural selection would have worked in an early RNA world.
			a. RNAs with stability and replicability are favored in vivo
			b. Complementary catalytic functions allow groups of RNAs
			c. These "quasispecies in hypercycle" could recombine into a single, multi-trait 
			molecule
			d. Covalent linkage with amino acids/peptides may have enhanced catalytic 
			function
	The origin of hereditary information made Darwinian evolution possible
	Debate about the origin of life abounds
		12. Describe the evidence that suggests that life first evolved on the sea floor near deep-
		sea vents.
			a. Surface waters were heavily irradiated and bombarded
			b. Abiotic syntheses of acetic acid, acetyl CoA, and sulfides of iron and nickel are 
			present near vents

THE MAJOR LINEAGES OF LIFE
	Introduction
	Arranging the diversity of life into the highest taxa is a work in progress
		13. Describe the basis for R. H. Whittaker's five-kingdom system.
			a. Sets prokaryotes apart
			b. Plants, animals and fungi separated by structure, life cycles, modes of 
			nutrition
			c. Protista includes leftovers and misfits
		14. List, distinguish among, and describe examples from each of the five kingdoms.
			a. Monera: prokaryotes
			b. Fungi: heterotrophs with external digestion
			c. Plants: multicellular autotrophs with tissues
			d. Animals: multicellular heterotrophs with internal digestion and tissues
			e. Protista: mainly unicellular eukaryotes
		15. Compare the three-domain system and R. H. Whittaker's five-kingdom system of 
		classification.
			a. Three domains based on nucleic acid and protein analysis
			b. Two domains of prokaryotes, Bacteria and Archaea, and the Eukarya