Biology 1406 Exam 6 History of Life - The Early Years
Living organisms have common structure (cells and cell structures)
1.3
Genetic information (DNA) determines structure
1.5, Ch 10
DNA → RNA → proteins ↓→ cell structure
→ enzymes control cell chemistry ( metabolism )
Mutations in DNA produce variation in living organisms of many traits - random
events, chance
Variation allows →↓ →
adaptation by natural selection
1.7, Ch 13
↓ [variations that increase reproductive success accumulate,
↓ other variations decrease - not chance ]
↓
→ speciation - populations that are isolated accumulate different
mutations; genetic differences increase through time prevent inter-reproduction Ch 14
- therefore life has a history of change
Ch 15
- well documented in fossil record, the “archive of living history”
13.4
What are fossils?
History of life closely intertwined with history of the earth - geology
15.7
- very dynamic system, life responds to change
- continental drift (Alfred Wegener, 1912)
- plate tectonics explains continental drift and most geological processes
Radiometric dating gives accurate time spans
15.5
- based on decay of naturally occurring radioactive elements
- halflife is time for 50% of atoms to decay - constant for atom
- while rock is molten crystals form with radioactive atom, not product
- crystal becomes “time capsule” trapping parent atom and daughter product
- strongly correlated to geological features
- accurate in rock of single age - volcanic ash and igneous (molten) rocks
- sedimentary rocks not reliable
Radioactive Parent Stable Product Half-life
uranium-238
lead-206
uranium-235
lead-207
thorium-232
lead-208
rubidium-87
strontium-87
potassium-40
argon-40
carbon-14
nitrogen-14
4,500 million
713
“
14,100 “
47,000 “
1,300 “
5,730 years
XXXXXXXXXXXX
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↓↓ 10 million years
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↓↓
10 million years
OOOOOOXXXXXX
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OOOOOOOOOOOO
OOOOOOOOOOOO
↓↓
10 million years
OOOOOOXXXXXX
OOOOOOOOOOOO
OOOOOOOOOOOO
OOOOOOOOOOOO
↓↓
10 million years
OOOOOOOOOXXX
OOOOOOOOOOOO
OOOOOOOOOOOO
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parent all
daughter none
parent 1/2
daughter 1/2
parent 1/4
daughter 3/4
parent 1/8
daughter 7/8
parent 1/16
daughter 15/16
History of Earth
15.1, 15.4
- formed about 4,600 mya (million years ago), with dense iron/nickel sinking to
form core, less dense mantle and even less dense crust
- cool enough by 3,900 mya for seas to form and gaseous atmosphere (CO2, N2,
H2S, H2; some CH4, NH3; no oxygen)
- oldest exposed rocks about 3,800 mya
- rocks from 3,500 mya contain fossils of several types of primitive bacteria
including stromatolite-forming cyanobacteria
- life probably arose between 3,900 and 3,500 mya
Formation of living system involves several steps:
15.1 - 15.3
- synthesis and accumulation of small organic molecules (A. Oparin 1920’s and
experiments of Stanley Miller and Harold Urey 1953)
- polymers (chains) from small molecules
- aggregation of molecules in a membrane
- self replication of the system (probably RNA)
- simple metabolism to gain energy
- any system like this could accumulate improvements through natural selection
- these steps very likely in reducing environment (electron giving) without oxygen
- in oxidizing environment organic molecules would break down quickly
What are ribozymes and why are they important ?
Modes of nutrition: prokaryotes have all variations
16.4
- all living organisms must obtain 2 resources: energy and nutrients to build new
molecules
- energy from several sources:
- simple inorganic reactions ex. H2S ---> H2 +S
(these compounds common in volcanic vents)
- breakdown of organic molecules
- light energy using photopigments
- nutrients from several sources:
- inorganic carbon dioxide (CO2)
- organic molecules (“fixed”, CHx )
- nitrogen is another important nutrient, but most organism can use only
fixed nitrogen (N-H or N-O), not N2
32.13
List the energy source and the nutrient source for each of the following modes of
nutrition. Include the organisms that use each mode.
chemoautotrophs chemoheterotrophs photoautotrophs photoheterotrophs -
One group of prokaryotes have outstanding history:
- cyanobacteria (blue-green bacteria) among oldest fossils, formed structures
called stromatolites
- photoautotrophs that can fix their own nitrogen (have two different type cells,
one photosynthesizing and the other fixing nitrogen)
- extremely common until about 1,000 mya; extensive fossil beds
- oxygen produced as byproduct of photosynthesis using water as an electron
source
- iron in solution until about 3,750 mya, then from 3,750 to about 2,000 mya
massive deposits of iron oxides (“rusting of the earth”) - thick banded iron
deposits found world wide
- indicates that large quantity of oxygen produced during this time period, most
absorbed in iron oxides (20 times as in atmosphere today)
- about 2,000 mya oxygen began accumulating in the atmosphere (iron depleted)
- cyanobacteria closely related to chloroplasts in plant and algae cells
Oxygen environment major catastrophe for life:
- deadly to most primitive bacteria
- allows more efficient metabolism - aerobic respiration 20 times more energy
than anaerobic respiration
- 1-2 levels in anaerobic food chain, 5-6 levels in aerobic food chain
- some primitive bacteria adapted to use oxygen
- ozone, O3, produced as byproduct of oxygen atmosphere, blocks ultraviolet
radiation
Living organisms divided into 3 domains
- Bacteria - (eubacteria)
- Archaea - (archaeabacteria)
- Eukarya - "protists", fungi, plants and animals
15.19
Prokaryotic cells: (Bacteria and Archaea)
16.1-12
- small (diameter 1-5 m)
- simple structure with no nucleus and generally little internal membranes
- have cell wall (chemically different from plants)
- many move by rotary flagellum, different from eukaryotic flagellum
- first fossils from 3,500 mya and numerous fossils to present
- only prokaryotes until about 2,200 mya, when eukaryotes appear and about 600
mya when multicellular organisms appear
- extremely common - anywhere there is life
- collective biomass of prokaryotes 10 times biomass of eukaryotes
- can accumulate DNA from other bacteria (horizontal gene transfer)
- complexes of interdependent bacteria develop, especially in anaerobic
environments; called biofilms or "consortium"
- more complex metabolism
- ex. sulfur consuming bacteria and methane consuming archaea
Archaea
- very common in anaerobic (without oxygen) environments similar to early earth:
“extremophiles”
- extreme halophiles live in high salt environments
- extreme thermophiles live in high temperature environments (boiling and above)
- acidophiles live in very acidic environments
- “lithophiles” in deep rock strata
- methanogens get energy by combining CO2 and H into methane in anaerobic
environment
- radiophiles can withstand extreme levels of radiation
- many species in non-extreme environments
Bacteria (eubacteria)
- most abundant group of living organisms on earth
- “gram-negative” and “gram-positive”
- some cause disease - toxins
- many harmless and symbiotic forms
- every form of nutrition
Eukaryotes
16.13 - .20
- larger cells with nucleus and internal membranes
- oldest fossils about 2,100 mya, common by 1,200 mya
- probably related to higher oxygen levels
- membrane infolding in “protoeukaryote”
- endosymbiosis with bacteria that could use oxygen for energy production
(became mitochondria); related to group of eubacteria
- then later with bacteria that could use light energy to fix carbon (became
chloroplast); related to cyanobacteria
- several features of mitochondria and plastids link them to primitive bacteria
- genetically similar: DNA, RNA and ribosomes
- method of division
- size and cell structure
- secondary endosymbiosis
- movement with cilia and flagella - “9 + 2” pattern
"Protists" - very diverse group of mostly single cell eukaryotes
- secondary endosymbiosis important in protist evolution
- several modes of nutrition in different groups
- different groups ancestors to multicellular groups (plant, animals and fungi)
- multicellular algae by 1.2 bya and soft body animals by 600 mya
- mass extinctions about 600 mya, then rapid expansion of multicellular forms