Chap 26 Early Earth and the Origin of Life. Hypotheses for Origin of Life on Earth Divine origin Extraterrestrial Origin Abiotic Origin.

Chap 26

Early Earth and the Origin of Life

Hypotheses for Origin of Life on Earth

• Divine origin

• Extraterrestrial Origin

• Abiotic Origin

Earth is part of the _______ __ Galaxy

The components for life are found in space.

Eg. Amino acids

Earth is part of the _______ __ Galaxy

The components for life are found in space.

Eg. Amino acids

443.83.8

3.53.5

221.71.7

.7.7

.475.475

• Alternatively, we can view these episodes with a clock analogy.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 26.2

Where did the first cell come from?

Could life come from non-life?

Spontaneous Generation of Life Abiogenesis

• In 1862, Louis Pasteur conducted broth experiments that rejected the idea of spontaneous generation even for microbes.

• A sterile broth would “spoil” only if microorganisms could invade from the environment. Fig. 26.9

Cells must come from pre-existing cells

BIOGENESIS

Ancient Reducing Atmosphere

• Oparin and Haldane proposed that Earth’s ancient atmosphere was reducing rather than oxidizing –providing an environment where Abiogenesis could take place.

• Why was there no free oxygen in Earth’s early atmosphere?

• Why would the first life not evolve in an oxidizing atmosphere?

P 494P 494

Miller and Urey simulated Earth’s early atmosphere

electricity simulated lightning

Why should they have used uV light?

Miller and Urey simulated Earth’s early atmosphere

electricity simulated lightning

Why should they have used uV light?

An alternate atmosphere contained carbon monoxide, carbon dioxide, nitrogen gas and water vapor

An alternate atmosphere contained carbon monoxide, carbon dioxide, nitrogen gas and water vapor

Experiments have produce all 20 amino acids, sugars, lipids, purines, pyrimidines

Experiments have produce all 20 amino acids, sugars, lipids, purines, pyrimidines

What is the importance of amino acids?

What is the importance of amino acids?

What is the importance of nucleic acids?

What is the importance of nucleic acids?

Lightning and uV light provided energy for polymerizationLightning and uV light provided energy for polymerization

Chemical EvolutionAbiogenesis

• Proposed by Oparin and Haldane

• The abiotic synthesis of monomers

• Polymerization of monomers

• Aggregation of molecules into protobionts

• Origin of heredity

Lightning and uV light provided energy for the formation of larger molecules and polymerization

Lightning and uV light provided energy for the formation of larger molecules and polymerization

Adenine is an important percursosr

Adenine is an important percursosr

Polymerization

• When monomers dripped on to hot sand, clay or rock polymerization can occur

• Clay concentrates amino acids and other monomers. Its charged surface can act as catalytic sites for polymerization.

• Pyrite can also act as catalytic sites for polymerization

P 495P 495

Polymerization led to proteins and nucleic acids such as RNAPolymerization led to proteins and nucleic acids such as RNA

• Liposomes behave dynamically, growing by engulfing smaller liposomes or “giving birth” to smaller liposomes.


Fig. 26.12a

• If enzymes are included among the ingredients, they are incorporated into the droplets.

• The protobionts are then able to absorbsubstrates fromtheir surroundingsand release theproducts of thereactions catalyzedby the enzymes.


Fig. 26.12b

Protobiont Examples

• Coacervate (Oparin) made of polypeptides nucleic acids and polysaccharides

• Proteinoid Micorspheres (Fox)

• Liposomes

Protobionts

• Aggregates of molecules that:• can start maintain a different internal environment

(homeostasis)• can show rudimentary metabolism (catalytic

reactions and modifications)• can show excitability (membrane potential)• can reproduce themselves• maintain genetic material

RNA could not only replicate itself, but it could also act as a catalyst

eg. Making proteins

RNA could not only replicate itself, but it could also act as a catalyst

eg. Making proteins

RNA with the best autocatalytic activity would predominate

RNA - First Genetic Molecule

RNA with the best autocatalytic activity would predominate

RNA - First Genetic Molecule

• Once primitive RNA genes and their polypeptide products were packaged within a membrane, the protobionts could have evolved as units.

• Molecular cooperation could be refined because favorable components were concentrated together, rather than spread throughout the surroundings.

6. Natural section could refine protobionts containing hereditary

information

Fig. 26.13

• Prokaryotes dominated evolutionary history from about 3.5 to 2.0 billion years ago.

• supports the hypothesis that the earliest organisms were prokaryotes.

• Relatively early, prokaryotes diverged into two main evolutionary branches, the bacteria and the archaea.– Representatives from both groups thrive in various

environments today.

2. Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years ago


Oldest fossil is of a bacteria 3.5 Billion years old

Oldest fossil is of a bacteria 3.5 Billion years old

What are stramatolites?

What are stramatolites?

• Two rich sources for early prokaryote fossils are stromatolites (fossilized layered microbial mats) and sediments from ancient hydrothermal vent habitats.– This indicates that the metabolism of prokaryotes

was already diverse over 3 billion years ago.

Fig. 26.4

• Photosynthesis probably evolved very early in prokaryotic history.– The metabolism of early versions of

photosynthesis did not split water and liberate oxygen.

3. Oxygen began accumulating in the atmosphere about 2.7 billion years ago


• Cyanobacteria, photosynthetic organisms that split water and produce O2 as a byproduct, evolved over 2.7 billion years ago.– This early oxygen initially reacted

with dissolved iron to form the precipitate iron oxide.• This can be seen today in banded iron

formations.

– About 2.7 billion years ago oxygen began accumulating in the atmosphere and terrestrial rocks with iron began oxidizing.


• While oxygen accumulation was gradual between 2.7 and 2.2 billion years ago, it shot up to 10% of current values shortly afterward.

• This “corrosive” O2 had an enormous impact on life, dooming many prokaryote groups.– Some species survived in habitats that remained

anaerobic.

• Other species evolved mechanisms to use O2 in cellular respiration, which uses oxygen to help harvest the energy stored in organic molecules.


• Eukaryotic cells are generally larger and more complex than prokaryotic cells.

• In part, this is due to the apparent presence of the descendents of “endosymbiotic prokaryotes” that evolved into mitochondria and chloroplasts.

4. Eukaryotic life began by 2.1 billion years ago


• While there is some evidence of earlier eukaryotic fossils, the first clear eukaryote appeared about 2.1 billion years ago.– Other evidence places the origin of eukaryotes to as

early as 2.7 billion years ago.

• This places the earliest eukaryotes at the same time as the oxygen revolution that changed the Earth’s environment so dramatically.– The evolution of chloroplasts may be part of the

explanation for this temporal correlation.– Another eukaryotic organelle, the mitochondrion,

turned the accumulating O2 to metabolic advantage through cellular respiration.


Aerobic bacteria

Ancient Prokaryotes

Ancient Anaerobic Prokaryote

Primitive Aerobic Eukaryote

Primitive Photosynthetic Eukaryote

Chloroplast

Photosynthetic bacteria

Nuclear envelope evolving Mitochondrion

Plants and plantlike protists

Animals, fungi, and non-plantlike protists

Section 17-2

Endosymbiotic Theory

Mitochondria and Chloroplasts are thought to have been engulfed by Archaea Bacteria and formed the first eukaryotic cells - 3 bya

Mitochondria and Chloroplasts are thought to have been engulfed by Archaea Bacteria and formed the first eukaryotic cells - 3 bya

• A great range of eukaryotic unicellular forms evolved into the diversity of present-day “protists.”

• Multicellular organisms, differentiating from a single-celled precursor, appear 1.2 billion years ago as fossils, or perhaps as early as 1.5 billion years ago from molecular clock estimates.

5. Multicellular eukaryotes evolved by 1.2 billion years ago

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.6

• Recent fossils finds from China have produced a diversity of algae and animals from 570 million years ago, including beautifully preserved embryos.


Fig. 26.7

• A second radiation of eukaryotic forms produced most of the major groups of animals during the early Cambrian period (after ice age).

• Cnidarians (the plylum that includes jellies) and poriferans (sponges) were already present in the late Precambrian.

6. Animal diversity exploded during the early Cambrian period

543 to 490 Million Years Ago

• The colonization of land was one of the pivotal milestones in the history of life.– There is fossil evidence that cyanobacteria and

other photosynthetic prokaryotes coated damp terrestrial surfaces well over a billion years ago.

– However, macroscopic life in the form of plants, fungi, and animals did not colonize land until about 500 million years ago, during the early Paleozoic era.

7. Plants, fungi, and animals colonized the land about 500 million years ago


Old 5 Kingdom Classification system lumped all prokaryotic organisms into Monera

Protista was found to be polyphyletic which led to it become broken up into smaller kingdoms

Two distinct lines of Prokaryotes leads to the Three Domain system.

Chap 26 Early Earth and the Origin of Life. Hypotheses for Origin of Life on Earth Divine origin Extraterrestrial Origin Abiotic Origin.

Documents

polymerization slide

origin of life slide

rna slide

cells biogenesis slide

benjamin cummings slide

important percursosr

amino acids earth

polymerization p