The History of Life

Question 1

The Hadean

Answer 1

ca 4600-3850 Ma

• Period from the origin of the solar system to about 3850 Ma
• No fossil record
• Almost no geologic record

Key Events:
• Differentiation of Earth into crust, mantle and core
• Origin of the atmosphere via volcanic outgassing (little free O2)
• Condensation of water vapor to form freshwater lakes, streams, etc. (likely acidic due to volcanic activity)
• Origin of continental crust (oldest dated rocks on earth are 3.96 billion years old)

Question 2

Differentiation of Earth into crust, mantle and core

Answer 2

Hadean

Question 3

Origin of the atmosphere via volcanic outgassing (little free O2)

Answer 3

Hadean

Question 4

Condensation of water vapor to form freshwater lakes, streams, etc. (likely acidic due to volcanic activity)

Answer 4

Hadean

Question 5

Origin of continental crust (oldest dated rocks on earth are 3.96 billion years old)

Answer 5

Hadean

Question 6

No fossil record.

Almost no geologic record.

Answer 6

Hadean

Question 7

What is “Life”?

Answer 7

Attributes of Life include:
• Autonomous replication - mitosis, meiosis; higher reproductive mechanisms
• Critical level of complexity - simpler subunits into multiple complex combinations
• Ability to evolve via natural selection?

Question 8

Requirements of life

Answer 8

• An energy source
• Basic chemicals (nucleic acids, proteins, minerals, etc.)
• An external environment that sustains life

Question 9

The Archean

Answer 9

(3850-2500 Ma)

• Origin of life (ca 3800 Ma)
• Early organisms had methane, SO4 (sulfate)andH2S (hydrogen sulfide) based metabolism, producing CO2 and alcohol as by-products.
• Photosynthetic organisms appear (ca 3500 Ma)
• Respired O2 accumulates and strengthens the ozone layer, trapping free oxygen below. The atmosphere is converted to an oxygen environment (3500-2800 Ma)

Question 10

Precambrian

Answer 10

Hadean
Archian
Proterozoic

Question 11

Earliest continents form from collision of smaller land masses (3400 Ma)

Answer 11

Archean

Question 12

Early life most likely consisted of

Answer 12

prokaryotic bacteria-like organisms

Question 13

Respired O2 accumulates and
strengthens the ozone layer,
trapping free oxygen below.
The atmosphere is converted to
an oxygen environment
(3500-2800 Ma)

Answer 13

Archean

Question 14

Early life most likely consisted of prokaryotic

bacteria-like organisms

Answer 14

Basically a capsule of genetic material

Question 15

Archaean Life

Answer 15

Various bacteria

Question 16

Thermus aquaticus

Answer 16

Thermus aquaticus is a species of small bacterium that can tolerate high temperatures, one of several thermophilic bacteria that belong to the Deinococcus-Thermus group.

Thermus aquaticus is a thermophilic gram-negative bacterium that has played a key role in the modern revolution in genetic research, genetic engineering, and biotechnology. Thermophilic bacteria are bacteria that thrive at very high temperatures, often above 45° C (113° F). Thermus aquaticus was originally isolated from a number of hot springs in Yellowstone National Park and a hot spring in California and was subsequently isolated from hot springs in other parts of the world and even from artificial hot water environments such as hot tap water. Previously, microbiologists had enriched for thermophilic bacteria at 55° C, but the discoverer of T. aquaticus, Thomas Brock, found that many thermophiles in his studies of microbial ecology would not be easily detected at such a “low” temperature since they require temperatures above 70° C to flourish. As Brock has noted, his discovery provides an excellent illustration of the often unpredictable value (both academic and applied) of basic research.

In the 1980s, a method known as the polymerase chain reaction (PCR) was developed to generate many copies of targeted segments of DNA from very tiny samples. This technique includes repeated cycles of melting apart of the two strands of each double-stranded DNA molecule (typically at 92° to 95° C) alternating with the extension of new complementary strands to create additional copies. To be practical, this method requires the use of a DNA polymerase that is not destroyed by this heating (DNA polymerases are enzymes that play a key role in DNA synthesis within cells). Fortunately, evolution has provided such polymerases in bacteria adapted to live at very high temperatures (e.g., in hot springs). Chien et al. (1976) had already purified a stable DNA polymerase from T. aquaticus with a temperature optimum of 80° C, which proved to serve very well for the automation of PCR.

The use of DNA polymerases from T. aquaticus and other thermophiles in PCR and related applications, such as DNA sequencing, has revolutionized biotechnology. The humble T. aquaticus enormously expanded what questions could be practically addressed in fields ranging from biomedical science (“what is the genetic basis for disease X and does this patient have this disorder?”) to animal behavior (“were all the young in this bluebird nest actually sired by the mother’s apparent mate?”) to conservation (“is this whale meat being sold truly from the species the seller claims?”) to forensics (“can this accused criminal possibly have left the DNA evidence found at the crime scene?”) and beyond.

http://eol.org/pages/974560/overview

Question 17

Thermus aquaticus

Answer 17

Thermus aquaticus is a species of small bacterium that can tolerate high temperatures, one of several thermophilic bacteria that belong to the Deinococcus-Thermus group.

Thermus aquaticus is a thermophilic gram-negative bacterium that has played a key role in the modern revolution in genetic research, genetic engineering, and biotechnology. Thermophilic bacteria are bacteria that thrive at very high temperatures, often above 45° C (113° F). Thermus aquaticus was originally isolated from a number of hot springs in Yellowstone National Park and a hot spring in California and was subsequently isolated from hot springs in other parts of the world and even from artificial hot water environments such as hot tap water. Previously, microbiologists had enriched for thermophilic bacteria at 55° C, but the discoverer of T. aquaticus, Thomas Brock, found that many thermophiles in his studies of microbial ecology would not be easily detected at such a “low” temperature since they require temperatures above 70° C to flourish. As Brock has noted, his discovery provides an excellent illustration of the often unpredictable value (both academic and applied) of basic research.

In the 1980s, a method known as the polymerase chain reaction (PCR) was developed to generate many copies of targeted segments of DNA from very tiny samples. This technique includes repeated cycles of melting apart of the two strands of each double-stranded DNA molecule (typically at 92° to 95° C) alternating with the extension of new complementary strands to create additional copies. To be practical, this method requires the use of a DNA polymerase that is not destroyed by this heating (DNA polymerases are enzymes that play a key role in DNA synthesis within cells). Fortunately, there are such polymerases in bacteria adapted to live at very high temperatures (e.g., in hot springs). Chien et al. had already purified a stable DNA polymerase from T. aquaticus with a temperature optimum of 80° C, which proved to serve very well for the automation of PCR.

The use of DNA polymerases from T. aquaticus and other thermophiles in PCR and related applications, such as DNA sequencing, has revolutionized biotechnology. The humble T. aquaticus enormously expanded what questions could be practically addressed in fields ranging from biomedical science (“what is the genetic basis for disease X and does this patient have this disorder?”) to animal behavior (“were all the young in this bluebird nest actually sired by the mother’s apparent mate?”) to conservation (“is this whale meat being sold truly from the species the seller claims?”) to forensics (“can this accused criminal possibly have left the DNA evidence found at the crime scene?”) and beyond.

http://eol.org/pages/974560/overview

Question 18

Archaea are ____

Answer 18

extremophiles

Question 19

Archaean Life:

Cyanobacteria

Answer 19

Cyanobacteria, also known as Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name “cyanobacteria” comes from the color of the bacteria.

Cyanobacteria are aquatic and photosynthetic, that is, they live in the water, and can manufacture their own food. Because they are bacteria, they are quite small and usually unicellular, though they often grow in colonies large enough to see. They have the distinction of being the oldest known fossils, more than 3.5 billion years old. Cyanobacteria are still around; they are one of the largest and most important groups of bacteria on earth.

Many Proterozoic oil deposits are attributed to the activity of cyanobacteria. They are also important providers of nitrogen fertilizer in the cultivation of rice and beans. The cyanobacteria have also been tremendously important in shaping the course of evolution and ecological change throughout earth’s history. The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras. Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today.

The other contribution of cyanobacteria is the origin of plants. The chloroplast with which plants make food for themselves is a cyanobacterium living within the plant’s cells. Sometime in the late Proterozoic, or in the early Cambrian, cyanobacteria began to take up residence within certain eukaryote cells, making food for the eukaryote host in return for a home. This event is known as endosymbiosis, and is also the origin of the eukaryotic mitochondrion.

Because they are photosynthetic and aquatic, cyanobacteria are often called “blue-green algae”. This name is convenient for talking about organisms in the water that make their own food, but does not reflect any relationship between the cyanobacteria and other organisms called algae. Cyanobacteria are relatives of the bacteria, not eukaryotes, and it is only the chloroplast in eukaryotic algae to which the cyanobacteria are related.

Question 20

Stromatolites

Answer 20

Stromatolites are formed from fossilized cyanobacteria

Question 21

The Proterozoic

Answer 21

(2500-542 Ma)
Origin of eukaryotes (1500 Ma).
Rapid diversification of soft-bodied multicellular animals and green algae (1500-600 Ma)

Question 22

Eukaryotic cell

Answer 22

Characteristics:
Nucleus - DNA storage, RNA transcription.
Membrane-bound organelles - compartmentalization of functions

Question 23

Serial Endosymbiosis Theory (SET)

Answer 23

Eukaryotic cells evolved when aerobic bacteria either infected or were engulfed by a larger host cell and later established a symbiotic relationship.

Question 24

Mitochondria are thought to be derived from

Answer 24

purple bacteria

Question 25

Chloroplasts are thought to be derived from

Answer 25

cyanobacteria

Question 26

Evidence for chloroplasts and mitochondria as endosymbiotic

organelles:

Answer 26

• Circular genomes in chloroplasts, mitochondria, and bacteria
• Mitochondria have cell membranes very similar to prokaryotes

Question 27

Progression toward multicellularity

Answer 27

Single-celled Eukaryotes&raquo_space; Colonial Eukaryotes

Volvox: many Chlamydomonas-like units
Porifera: Choanoflagellate-derived units

Colonial Eukaryotes&raquo_space; Differentiated Multicellular Eukaryotes

Question 28

Challenges of Multicellularity

Answer 28

• Need for support, rigidity, increases.
• Reproduction becomes more difficult.

• Surface to Volume ratio (S/V) goes down as size increases
– Surface controls exchange with environment

• Diffusion, heat exchange, area that might contact food, all dependent on S
– Metabolic demands (O2, CO2, energy) largely dependent on V (or, equivalently, M)

• Animals adjust S/V by shape
• Use bulk transport to supplement diffusion for long-distance movement of materials

Question 29

Challenges of Multicellularity

Answer 29

• Need for support, rigidity, increases.
• Reproduction becomes more difficult.

• Surface to Volume ratio (S/V) goes down as size increases
– Surface controls exchange with environment.
– Diffusion, heat exchange, area that might contact food, all dependent on S.
– Metabolic demands (O2, CO2, energy) largely dependent on V (or, equivalently, M).
– Animals adjust S/V by shape.
– Use bulk transport to supplement diffusion for long-distance movement of materials.

Question 30

Opportunities of Multicellularity

Answer 30

Cellular and tissue specialization (greater
complexity) becomes possible
– Specialization and compartmentalization
– Epidermal layer to keep interior from drying, protect
from microbial invasion, etc.
– Skeleton for support, movement
– Vascular system to transport gasses and nutrients
– Distinct reproductive cells, tissues, organs

Question 31

Cambrian explosion

Answer 31

Relatively sudden appearance of diverse animal forms in fossil record ~450 mya.

Fossils of many phyla first appear in the early Cambrian (542 to ~ 530 mya)

First fossil evidence of each animal phylum

Question 32

First fossil evidence of each animal phylum

Answer 32

Cambrian explosion

Question 33

The Cambrian Explosion (cont.)

Answer 33

• The “sudden” appearance of so many
different types of animals raises a number of
questions.
– Earlier fossils have been found, but these are of
small animals or protists (cysts) without easily
fossilizable (hard) parts

• The Cambrian is represented by several
“Lagerstätten” where soft-bodied animals
have been preserved
– E.g., the Burgess Shale (next slide)
• By the end of the Cambrian, all “major” phyla
(perhaps all phyla) were present

Question 34

The Cambrian Explosion (cont.)

Answer 34

• The “sudden” appearance of so many different types of animals raises a number of questions.
– Earlier fossils have been found, but these are of
small animals or protists (cysts) without easily
fossilizable (hard) parts

• The Cambrian is represented by several
“Lagerstätten” where soft-bodied animals have been preserved
– E.g., the Burgess Shale

• By the end of the Cambrian, all “major” phyla (perhaps all phyla) were present

Question 35

Lagerstätte

Answer 35

A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues.

Question 36

The Burgess Shale Fauna

Answer 36

Pikaia (a chordate)
Marella (an arthropod)
Anomalocaris (phylum?)
Priapulid worm
Hallucigenia (an onycophoran?)

Question 37

Explanations for the Cambrian explosion fall into 2 categories

Answer 37

– Intrinsic: something about animals changed, e.g., new developmental patterns
– Extrinsic: something about the environment changed, e.g., increase in available oxygen

Question 38

Intrinsic

Answer 38

something about animals changed, e.g., new

developmental patterns

Question 39

Extrinsic

Answer 39

something about the environment changed, e.g., increase in available oxygen

Question 40

Intrinsic Explanations

Answer 40

Hox and Hox-like

genes

Question 41

Hox and Hox-like genes

Answer 41

• Hox and Hox-like genes were duplicated in the
bilaterians
– The number of such genes correlates with complexity

Question 42

Extrinsic Explanations

Answer 42

• So if we accept the idea (at least tentatively) that animals had the genetic mechanisms to
become large well before the Cambrian, why didn’t they?
– Here we may need to look at extrinsic explanations of diversification

Extrinsic Explanations (cont.)
• Ancient atmosphere contained insufficient O2 to allow evolution of active life styles
– O2 didn’t approach current levels until sometime in the Ediacaran
– Without sufficient O2, large animals are possible, but not large, active animals
– This may be the reason there are reasonably large animals in the Ediacaran, but not, apparently, very active ones

Extrinsic Explanations (cont.)
• Possibly a mass extinction of the former biota
allowed new forms to radiate at the start of the
Cambrian
– This has happened after previous mass extinctions
– We know the Ediacaran animals disappeared
rapidly just before the Cambrian, but whether this
was due to a mass extinction is not yet certain

• Another ecological explanation envisions an
ecosystem that reached a tipping point in
complexity resulting in widespread co-evolution
– For instance, there may have been an “arms race” between predator and prey
• Each advance in predatory ability requires a
countermeasure by prey, and vice versa
– Greater incorporation of mineralized hard parts
may have started such an arms race
• This would also explain the sudden appearance of fossils at this time

Question 43

There are two prevailing streams of thought which attempt to explain life’s origins:

Answer 43

Questions remain:
– Which explanations are relevant? (All of them?)
– Why no new phyla (or at least “major” phyla)
since the Cambrian?

• Life originated from abiotic precursors that existed here on Earth
– “ABIOGENESIS”

• Life on Earth originated from biotic or abiotic precursors that arrived from extraterrestrial sources – “PANSPERMIA”

Question 44

ABIOGENESIS

Answer 44

Life originated from abiotic precursors that existed here on Earth

Question 45

PANSPERMIA

Answer 45

Life on Earth originated from biotic or abiotic precursors that
arrived from extraterrestrial sources

Question 46

T. H. Huxley, “Biogenesis and Abiogenesis” (1870)

Answer 46

“…and I shall term the contrary doctrine–that living matter may be produced by not living matter–the hypothesis of Abiogenesis.”

Question 47

the hypothesis of Abiogenesis

Answer 47

The physicist John Desmond Bernal (1901-1971) suggested 3 clearly defined stages that could be recognized in explaining life’s origins

Stage 1 - The origin of biological monomers
Stage 2 - The origin of biological polymers
Stage 3 - The evolution from molecules to cell

Question 48

Miller-Urey Experiment

Answer 48

Synthesized organic compounds from inorganic precursors

Question 49

The prebiotic world consisted of a wide array of organic molecules

Answer 49

Many of these were in the form of nucleic acids, which could form simple oligonucleotides

Reactive nucleotides form&raquo_space; Minerals catalyze
polymer formation&raquo_space; Random strands of RNA
(Catalyst and a Noncatalyst)

Question 50

Modern Abiogenesis: the “RNA World” hypothesis

Answer 50

• Early life was based on RNA
• Likely short-lived (ca 1 billion years) once oxygen became abundant and DNA-based life became prevalent.
• DNA has much lower mutation rate? Favors stability of DNA.

Question 51

William Thompson (Lord Kelvin), Address to the B. A. A. S. (1871)

Answer 51

…we must regard it as probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space. If at the present instance no life existed upon this earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation.

Question 52

Panspermia Hypothesis

Answer 52

Earth is continuously bombarded with material from interstellar space, much of it consisting of organic compounds. These may have provided the
basic building blocks of life.

Question 53

Murchison meteorite

Answer 53

The Murchison meteorite is named after Murchison, Victoria, in Australia. It is one of the most studied meteorites due to its large mass, the fact that it was an observed fall, and that it belongs to a group of meteorites rich in organic compounds.

Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth.

Chondrite, Parent body
Isovaline is a rare amino acid transported to earth by the Murchison meteorite, which landed in Australia in 1969.

www.meteorman.org/ Murchison_16_Tim_Heitz.jpg

Question 54

Taq Polymerase

Answer 54

Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated by Thomas D. Brock in 1965.

A heat stable dNA polymerase that is normally used in the polymerase chain reaction. It was isolated from Thermobius aquaticus.