Topic 9: Origin of Life Flashcards
The three main biological polymers,
nucleic acids, proteins, and
polysaccharides, are built from:
five
nucleotide bases, 20 amino acids, and
a few sugars
What an entity needs to be considered alive:
Organization, metabolism, stimuli, homeostasis, adaptation, reproduction
Organization
structurally
composed of one or more cells
(basic units of life)
Metabolism
a system of
management of energy and
materials via chemical reactions
Stimuli
Response to stimuli: via changes in
growth, alteration of chemical
reactions, or movement
Homeostasis
maintenance of
some internal chemical and/or
thermal consistency relative to
variation outside of the organism
Adaptation
the ability to change
over time in response to the
environment
Reproduction
ability to produce
new individual organisms
Viruses
- have nucleic acids that can replicate, mutate, and respond to natural selection
- lack metabolism and homeostasis, and cannot reproduce without using the cellular machinery of a host cell
Earth formed ___ years ago
4.6 billion
First replicating life:
3.9 billion years ago
The geologic record is divided into:
the Archaean, the Proterozoic, and
the Phanerozoic eons
Three eras of phanerozoic
Paleozoic, Mesozoic, and Cenozoic
Fossils
the preserved
remains/evidence of organisms that
lived in the past.
Fossils are used for:
calibrate
phylogenies, record extinct species (e.g.
linkage between dinosaurs and modern
birds), and link evolutionary events (e.g.
mass extinctions) with geological and
environmental changes on Earth.
Probability of an organism (or part of)
becoming fossilized increases if:
- Existed for a long time.
- Was abundant and widespread.
- Hard rather than soft-bodied.
- Aquatic rather than terrestrial.
- Inshore marine rather than offshore
marine. - Decomposing organisms were absent
Types of fossils recorded
Cast, Replacement, trace, preserved
Cast fossils
A cast forms when minerals fill
space in sediment where the
organism decayed after having
been buried
Replacement fossil
fossils
have had their tissues replaced by
minerals
Trace fossils
record evidence of
behavior (tracks, burrows, feces).
Preserved fossils
retain the original
organic material (carbon films,
amber, tar or peat, frozen)
Sedimentary strata reveal ____
ages of fossils
relative
Radioactive dating
Radioactive decay of isotopes of various elements provides a means of determining the age of fossils or rocks. Radioactive isotopes decay from one form to another at a known constant rate.
Half life of C14
5,730 years
time when there was a supercontinent
1.1 billion, 600
million, and 250 million years ago.
Plate tectonics theory
considers that Earth’s crust is composed of large plates that have been slowly moving since about 3.4 billion years ago
Continental drift during pangea
- Deepening of ocean basins.
− Reduction in shallow water habitats.
− Colder and drier climate inland.
Continental drift effect on biodiversity
- Changes to the environment and climate as
continents move north or south.
− Opportunities for diversification. (e.g. when land masses are isolated, each can develop unique
species via allopatric speciation.)
− Mass extinctions.
The fossil record shows that most
species that have ever lived are
now ___
extinct
In each of the 5 mass extinctions, ___ of species went extinct
50%
Permian mass extinction
- the boundary between the Paleozoic and Mesozoic eras
- 252 million years ago
- greatest extinction
- caused by extensive volcanism in Siberia
- during formation of Pangea (more shallow shorelines and reduced temperature gradient)
Cretaceous mass extinction
- separates Mesozoic from Cenozoic
- 65.5 million years
- 20% of families went extinct
- extinction of dinos
- Presence of iridium in sedimentary rocks suggests a massive meteorite impact about 65 mya
It can take ____ years for biodiversity to recover after a mass-extinction
5 to 100 million
years
Mass extinctions can lead to
adaptive radiation
Adaptive radiation
the rapid
evolution of diversely adapted
species from an ancestral species
When does adaptive radiation happen
Adaptive radiation occurs when a
change in the environment makes
new ecological niches available
Adaptive radiations may follow
mass extinctions, the evolution of novel characteristics, colonization of new regions
Mass extinctions
By eliminating so many species, mass
extinctions can pave the way for
adaptive radiations
Evolution of novel characteristics
The adaptive radiation of
photosynthetic prokaryotes, land
plants, insects, and tetrapods was
enabled by novel adaptations
Colonization of new regions
Adaptive radiations can occur when
organisms colonize new
environments with little competition
Earth’s first billion years
- The surface began to cool; unstable crust floated on the molten magma.
- Steaming gasses from cooling rock formed an atmosphere lacking oxygen.
- Atmospheric temperatures dropped:
gasses condensed and rained down. - Basins filled with water, forming transient
oceans. - Between 3.8 and 4.1 bya bombardment of Earth by asteroids and comets would have vaporized water, preventing seas from forming and sterilizing the planet’s surface
- Earth’s early atmosphere likely contained water vapour and chemicals from volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia,
hydrogen, hydrogen sulphide)
hypothesized
sequence of stages for evolution of simple cells
1. Abiotic synthesis of small organic molecules. 2. Joining of small organic molecules into organic polymers (organic macromolecules). 3. Packaging of molecules into protocells. 4. Origin of self-replicating molecules.
Abiotic synthesis of small organic molecules
inorganic to organic
- possibly due to terrestrial origins or extraterrestrial oragins
Terrestrial origins of organic molecules on earth
organic molecule synthesis driven by energy sources, e.g. UV light, electrical discharges. Earth’s early atmosphere was initially hypothesized to be a reducing environment.
Miller & Urey demonstrated:
the abiotic synthesis of organic molecules in a reducing atmosphere
Instead of forming in the
atmosphere, abiotic synthesis may
have occurred:
near volcanoes or
deep-sea hydrothermal vents where
strongly reducing conditions are
found
Abiotic synthesis of organic polymers
Wetting and drying cycles of water on hot surfaces, such sand, clay, or rock, may have concentrated small organic molecules, triggering the spontaneous formation of organic polymers
Polyphosphates cause polymerization
of amino acids into
peptides
Packaging of molecules into protocells
- Free-floating amino acids, proteins, and nucleic acids would not have been able to behave like cells - there needed to be replication and metabolism - In water, lipids and other organic molecules can spontaneously form hollow vesicles with a lipid bilayer A sphere would have been able to keep (or export) its products
− Protocells
fluid-filled
vesicles with a membrane-like
structure
w lipid vesicles form faster in the presence of
volcanic clay
Lipid vesicles exhibit
simple reproduction and metabolism, and can maintain an internal chemical environment. Vesicles can increase in size and divide on their own.
earliest genetic material was
RNA
RNA
- RNA is single-stranded, fragile, and self-replicating. − RNA can store genetic information. − Self-replicating RNA molecules have been experimentally demonstrated. − RNA could have provided a template for the later evolution of DNA, a more stable genetic material
Some RNA molecules (ribosomes) can catalyze ______
chemical reactions
The oldest fossil evidence of life is
of
prokaryotes (~3.5-3.7 bya)
Prokaryotes
− Single-celled (unicellular).
− DNA is not contained in a nucleus.
− Lack membrane-bound organelles
Two domains of prokaryotes
bacteria and archaea
The oldest known fossils are
stromatolites
Stromatolites
rocks formed by the accumulation of sedimentary layers on prokaryote mats (date back to 3.5-
3.7 bya)
Oxygen revolution
− Oxygen began accumulating in the atmosphere ~2.7 bya. − Oceanic photosynthetic prokaryotes (cyanobacteria) used the sun’s energy to fix CO2, producing O2 as a byproduct. − Initially, O2 produced by cyanobacteria reacted with iron dissolved in oceans, precipitating to form banded iron formations
Earth’s early prokaryotes evolved in O
2-free conditions and used
anaerobic metabolism
