Early Earth and

the Origin of Life

chapter 26

First 3/4 of evolutionary history- organisms were microscopic

*based on molecular clocks.

Louis Pasteur

• Spontaneous Generation (FALSE)

• Biogenesis (TRUE)

• Boiling broth experiments.

Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 1)

Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 2)

Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 3)

Four-Stage Hypothesis for the Origin of Life

1. Abiotic synthesis of small organic molecules, such as amino acids and nucleotides.

2. Joining of small molecules (monomers) into polymers, including proteins and nucleic acids.

3. Origin of self-replicating molecules that eventually made inheritance possible

4. Packaging of these molecules into “protobionts” droplets with membranes that maintained an internal chemistry different from the surroundings.

OVERVIEW (not on outline)

Early Earth…

1. The Earth and its atmosphere formed• Gasses present when the atmosphere was first

formed: Produced by volcanic out gassing. Gases produced were

probably similar to those created by modern volcanoes • H2O (water), H2 (hydrogen gas) NH3 (ammonia) and CH4

(methane) = WHAM! also: CO2, SO2, CO, S2, Cl2, N2,

• No free O2 at this time (not found in volcanic gases).– A.I. Oparin and J.B.S. Haldane independently theorized that

simple molecules were able to form only because oxygen was absent. Stanley Miller later tests this idea.

– As a very reactive molecule, oxygen, had it been present, would have prevented the formation of organic molecules by supplanting most reactants in chemical reactions.

BIOCHEMICAL EVOLUTION

2) The primordial seas formed.• As the earth cooled, gases

condensed (beginning of hydrologic cycle) to form oceans/ seas consisting of water and minerals.

3) Complex molecules were synthesized.

• Chemicals present in the ancient seas:

• Acetic acid, formaldehyde, and amino acids.

• These kinds of molecules would later serve as monomers, or unit building blocks, for polymers like protein.

How were the first organic molecules created?

1. An organic “soup” formed. Creation of organic molecules (ex. amino acids) from inorganic molecules (WHAM!).

2. Energy sources: ultraviolet light (UV), lightening, radioactivity, & heat- hydrothermal vents (hot volcanic outlets in the deep-sea floor) drove the reactions. NO ENZYMES WERE NEEDED.

Stanley Miller and Harold Urey (1953)tested the theories of Oparin & Haldane

• Using an airtight apparatus, H2O, H2, NH3 (ammonia), CH4 (methane), and a high voltage discharge, they found that after one week the water contained various organic molecules including amino acids.

• The amino acids synthesized are the building blocks of proteins for organisms.– Proteinoids are abiotically produced

polypeptides. They can be experimentally produced by allowing amino acids to dehydrate on hot, dry substrates.

• Adenine (another organic molecule) and other nucleotides are the building blocks of RNA (also- Adenine for ATP).

The Earliest “Cells” = protobionts

• Organic molecules were concentrated and isolated into protobionts “proto-life”.

• Under the appropriate conditions, a mixture of amino acids, carbohydrates & lipids will spontaneously form a microsphere or coacervate by self-assembly.

Figure 26.13 Hypothesis for the beginnings of molecular cooperation

• These coacervates – tiny spherical droplet of

assorted organic molecules-specifically, lipids which is held together by hydrophobic forces from a surrounding liquid.

– Can reproduce– can carry out chemical

reactions enclosed within border across which materials can be exchanged. (

• Microspheres can also hold enzymes, nutrients, polymers.

The Earliest Catalysts• “RNA world” preceded today’s “DNA world”.• RNA based enzymes that extracted energy from inorganic

sulfur compounds taken up from the surroundings.• This energy could be used for other reactions within the

protobiont- including the replication of RNA.• “RNA world” gave way to a “DNA world”

Primitive Cells• Oldest rocks 3.8 billion years old, located at a site

called Isua, in Greenland… some chemical clues that life might have existed but no fossils found.

• Oldest fossils located in rocks from western Australia that are 3.5 billion years old.

Figure 26.3x1 Spheroidal Gunflint Microfossils

• Found in stromatolites, fossilized mats similar to layered microbial mats that certain groups form in salt marshes and warm lagoons.

• Diverged into two groups:

1. Bacteria2. Archeae

Unnumbered Figure (page 512) Evolutionary clock: Prokaryotes

Significant prokaryotic diversity existed 3BYA

Metabolism1st anaerobic heterotrophismThen photosynthesis

• Prokaryotic Heterotrophs feeding on organic molecules in the seas began to develop metabolism.

• The first form of metabolism (fermentation) most likely arose because the atmosphere lacked free oxygen. Anaerobic

• What was to follow… would change the earth significantly

Autotrophic Evolution… evolved very early in prokaryotic history.

• The first autotrophs were probably nonoxygenic photosynthesizers. They did not split water and liberate oxygen. (cyclic only)

• The first organisms to use noncyclic photosynthesis or oxygenic photosynthesis (water-splitting enzyme) were probably cyanobacteria evolved over 2.7 billion years ago.

• Cyanobacteria are the only photosynthetic prokaryotes that generate oxygen.

Unnumbered Figure (page 513) Evolutionary clock: Atmospheric oxygen

• A byproduct of oxygenic photosynthesis was oxygen and as it accumulated in the atmosphere (2.7-2.2 billion years ago),

1. First dissolved into the surrounding water until the seas and lakes became saturated with oxygen.

2. Additional oxygen would then react with dissolved iron and precipitate as iron oxide.

Figure 26.5 Banded iron formations are evidence of the vintage of oxygenic photosynthesis

3. Then additional oxygen finally began to “gas out” of the seas etc. and accumulate in the atmosphere.

• the ozone layer was created.

• As the ozone absorbed UV rays, the major source of energy for abiotic synthesis of organic molecules and primitive cells was terminated.

Additionally… the oxygen itself had tremendous impact

• Corrosive O2 attacks chemical bonds, doomed many prokaryotes.

• Some survived in anaerobic environments (obligate anaerobe survivors)

• Others adapted- cellular respiration.

Unnumbered Figure (page 514) Evolutionary clock: Eukaryotes

2.1 BYA1st EUKARYOTES

The first eukaryotic organelles evolved from prokaryotes

(2.1 billion years ago)• Mitochondria and Chloroplasts are

descendents of “endosymbionts”- symbiotic cells living within larger host cells.

• Many eukaryotes may have evolved from prokaryotes enjoying a mutually beneficial relationship (symbiosis).

• Endosymbiotic theory- Margulis.

Fossilized algae

evidence1. Mitochondria and chloroplasts resemble

bacteria and cyanobacteria with respect to their DNA, RNA, and protein synthesis machinery.

2. Mitochondria and chloroplasts reproduce independently of their eukaryotic host cell.

3. Ribosomes of mitochondria and chloroplasts reproduce independently of their eukaryotic host cell.

4. The thylakoid membranes of chloroplasts resemble the photosynthetic membranes of cyanobacteria.

Precambrian fossils reveal:• Diversity of unicellular forms- protists and

other single celled descendants.• Examples:• 1.2 billion years ago Multicellular algae,

Plants, Fungi• 600 mya Animals had diverged to form

the diversity of invertebrates known today.

• Snowball Earth hypothesis- the Earth's surface became nearly or entirely frozen at least once, some time earlier than 650 million years ago… confined life to areas near deep-sea vents and hot springs…

Fossilized animal embryos

Unnumbered Figure (page 514) Evolutionary clock: Multicellular eukaryotes

1.2 BYA1st MULTICELLULAREukaryotes

Unnumbered Figure (page 515) Evolutionary clock: Animals

Unnumbered Figure (page 515) Evolutionary clock: Land plants

Cambrian explosion (550 mya):• After seemingly slow evolution (3 billion years) of prokaryotes and simple eukaryotes the cambrian explosion was the relatively rapid

appearance (millions of years) of most major phyla.• ANIMALS:• Porifera, Cnidaria, • Mollusca• Platyhelminthes, • Nematoda, Annelida, • Arthropoda,

• Echinodermata & Chordata

Figure 26.8 The Cambrian radiation of animals

Figure 26.14 A window to early life?

Figure 26.15 Whittaker’s five-kingdom system

Figure 26.16 Our changing view of biological diversity

Figure 26.0x Volcanic activity and lightning associated with the birth of the island of

Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth