Origin of Life Hypotheses

Origin of Life Hypotheses Evolutionary Theory

A. The Early Earth and Earth History 4.5 bya: Earth Forms Graviational sorting of materials…heavy to the core, gases released under pressure…

The Early Earth and Earth History - Earliest Atmosphere - probably of volcanic origin Gases produced were probably similar to those released by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 and CH4

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils Stromatolites - communities of layered 'bacteria'

A. The Early Earth and Earth History 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils Putative microfossil bacteria from Australia that date to 3.4 by

- the first cells were probably heterotrophs that simply absorbed nutrients and ATP from the environment. - as these substances became rare, there was strong selection for cells that could manufacture their own energy storage molecules. - the most primitive cells are methanogens (Archaea), but these are NOT the oldest fossils.

- the second type of cells were probably like green-sulphur bacteria, which used H2S as an electron donor, in the presence of sunlight, to photosynthesize.

IV. Early Life - about 3.2 bya, “banded iron” formations occur… these are formed by the oxidation of dissolved iron and Sulphur … removal of electrons by primitive ‘non-oxygenic’ photosynthesis, resulting in rusty precipitates of iron .

A. The Early Earth and Earth History “Red Beds” 2.3-2.0 bya: Oxygen in Atmosphere 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

- the evolution of oxygenic photosynthesis was MAJOR - the evolution of oxygenic photosynthesis was MAJOR. It allowed life to exploit more habitats, and it produced a powerful oxidating agent!

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

Eukaryote Characteristics - membrane bound nucleus - organelles - sexual reproduction

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 0.065 bya:Cenozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

A. The Early Earth and Earth History 4.5 million to present (1/1000th of earth history) 2.3-2.0 bya: Oxygen 1.8 bya: first eukaryote 0.9 bya: first animals 0.5 bya: Cambrian 0.24 bya:Mesozoic 0.065 bya:Cenozoic 4.5 bya: Earth Forms 4.0 bya: Oldest Rocks 3.4 bya: Oldest Fossils

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously Aleksandr Oparin (1894-1980) J.B.S. Haldane (1892-1964)

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) all biologically important monomers have been produced by these experiments, even while changing gas composition and energy sources

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) - Sydney Fox - 1970 - polymerized protein microspheres

B. The Formation of Biologically Important Molecules - Oparin-Haldane Hypothesis (1924): - in a reducing atmosphere, biomonomers would form spontaneously - Miller-Urey (1953) - Sydney Fox - 1970 - polymerized protein microspheres - Cairns-Smith (1960-70) - clays as templates for non-random polymerization - 1969 - Murcheson meteorite - amino acids present; some not found on Earth. To date, 74 meteoric AA's. - 2004 - Szostak - clays could catalyze formation of RNA's

C. Acquiring the Characteristics of Life Three Primary Attributes: - Barrier (phospholipid membrane) - Metabolism (reaction pathways) - Genetic System

C. Acquiring the Characteristics of Life 1. Evolution of a Membrane - form spontaneously in aqueous solutions

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - problem: how can pathways with useless intermediates evolve? These represent 'maladaptive valleys', don't they? A B C D E How do you get from A to E, if B, C, and D are non-functional?

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution A B C D E

E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution suppose E is a useful molecule, initially available in the env. E

E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution suppose E is a useful molecule, initially available in the env. As protocells gobble it up, the concentration drops. E

D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution Anything that can absorb something else (D) and MAKE E is at a selective advantage... D E

D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution Anything that can absorb something else (D) and MAKE E is at a selective advantage... but over time, D may drop in concentration... D E

C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution So, anything that can absorb C and then make D and E will be selected for... C D E

A B C D E C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways - Solution - reverse evolution A B C D E and so on until a complete pathway evolves.

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? DNA RNA (m, r, t) protein

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? DNA DNA stores info, but proteins are the metabolic catalysts... RNA (m, r, t) protein

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? - Ribozymes info storage AND cataylic ability

C. Acquiring the Characteristics of Life Evolution of a Membrane Metabolic Pathways Evolution of a Genetic System - conundrum... which came first, DNA or the proteins they encode? - Ribozymes - Self replicating molecules - three stage hypothesis

Stage 1: Self-replicating RNA evolves

(REPLICATION ENZYMES) Stage 1: Self-replicating RNA evolves RNA m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 2: RNA molecules interact to produce proteins... if these proteins assist replication (enzymes), then THIS RNA will have a selective (replication/reproductive) advantage... chemical selection.

(REPLICATION ENZYMES) DNA Reverse transcriptases m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

Can this happen? Are their organisms that read RNA and make DNA?

Can this happen? Are their organisms that read RNA and make DNA? yes - retroviruses....

(REPLICATION ENZYMES) DNA m- , r- , and t- RNA Already have enzymes that can make RNA... PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

(REPLICATION ENZYMES) DNA m- , r- , and t- RNA Already have enzymes that can make RNA... PROTEINS (REPLICATION ENZYMES) Stage 3: Mutations create new proteins that read RNA and make DNA; existing replication enzymes replicate the DNA and transcribe RNA.

(REPLICATION ENZYMES) This is adaptive because the two-step process is more productive, and DNA is more stable (less prone to mutation). DNA m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 4: Mutations create new proteins that replicate the DNA instead of replicating the RNA...

(REPLICATION ENZYMES) This is adaptive because the two-step process is more productive, and DNA is more stable (less prone to mutation). DNA And that's the system we have today.... m- , r- , and t- RNA PROTEINS (REPLICATION ENZYMES) Stage 4: Mutations create new proteins that replicate the DNA instead of replicating the RNA...

D. Summary: STEPS REQUIRED FOR THE SPONTANEOUS, NATURAL FORMATION OF LIFE, and the evidence to date: 1. Spontaneous synthesis of biomolecules - strong evidence; Miller-Urey experiments. 2. Polymerization of monomers into polymers (proteins, RNA, sugars, fats, etc.) - strong evidence;  Fox and Cairns-Smith experiments. 3. Formation of membranes - strong evidence; behavior of phospholipids in solution. 4. Evolution of metabolic systems - reasonable hypotheses, and genetic similarity in genes involved in particular pathways (suggesting gene duplication and subsequent evolution of new genes and elaboration of existing pathways) 5. Evolution of a genetic system - a reasonable hypothesis and significant corroborating evidence that it could happen. But no experimental evidence of the process evolving through all three steps. 6. How did these three elements (membrane, metabolism, genetic system come together?) a few untested hypotheses.

IV. Early Life Woese - r-RNA analyses reveal a deep divide within the bacteria

IV. Early Life

IV. Early Life

IV. Early Life Curiously, the very root of life may be invisible to genetic analysis. Bacteria transfer genes by division (to 'offspring'), but they also transfer genes "laterally" to other living bacteria. This makes reconstructing bacterial phylogenies difficult.

IV. Early Life So, reconstructing the patterns of relatedness among these ancient life forms is difficult. Different genes give different patterns of relatedness among domains

IV. Early Life C. Domains - "Ring of Life" hypothesis (2004)