Lecture 12 History of Life on Earth Flashcards
How has life on Earth changed over time?
slide 3
How has life on Earth changed over time?
Past organisms were very different from those presently living
–For example, fossils found in the Saharan Desert document the transition of whales from land to sea
What is Macroevolution?
Evolutionary patterns on a larger scale
Cumulative effect of many speciation and extinction events
Example: emergence of terrestrial vertebrates
1. series of speciation events,
2. the impact of mass extinctions on biodiversity,
3. origin of key adaptations such as flight
5 patterns of macroevolution
– Stasis
– Exaptation
– Mass extinction
– Adaptive radiation
– Coevolution
Macroevolution
- Evolutionary patterns on a larger scale
- Cumulative effect of many speciation and extinction events
The fossil record shows macroevolutionary
changes over large time scales, for example:
* the emergence of terrestrial vertebrates
* the impact of mass extinctions
* the origin of key adaptations, such as flight
1.Conditions on early Earth (creating molecules)
Chemical and physical processes
could produce simple cells
through 4 stages
- Abiotic synthesis of small organic
molecules - Joining of these small molecules
into macromolecules - Packaging of molecules into
protocells, droplets with
membranes that maintain an
internal chemistry different from
the environment - Origin of self-replicating
molecules
slide 7
How do we know the conditions on the early Earth?
slide 8-10
- The fossil record
- Reveals changes in the history of life on Earth
- Accumulation of fossils in sedimentary rock
layers, called strata
slide 11-13
Fossil records
Analysis:
* Many past organisms were unlike those living today
* Many organisms once common are now extinct
* New groups arose from previously existing ones
Incomplete record
* Few organisms were preserved as fossils
* Many fossils were destroyed by geologic processes
* Only a fraction of fossils have yet been discovered
Dating Rocks and Fossils
- The order of fossils in rock strata tells us the
sequence in which they were formed - We can infer relative ages of fossils using thismethod, but not their actual ages
- Radiometric dating:determine the age of
fossils based on the decay of radioactive
isotopes - A radioactive “parent” isotope decays to a
“daughter” isotope at a characteristic rate - Half-life of isotope = time needed for 50% ofthe parent isotope to decay (known value)
Radiometric dating
slide 16
Using Ratio of C-14 to C-12
● Used to date fossils
up to 75,000 yrs old
● C-12 stable; the
amount in the
organism does not
change after its death
● C-14 radioactive;
slowly decays to N-14
after the organism’s
death
slide 18-20
The Geologic Record
Divides Earth’s history
into four eons
* Hadean
* Archean
* Proterozoic
* Phanerozoic
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- Key events in life’s history
- Single-celled prokaryotes (in the ocean)
Similar to cyanobacteria - Oxygen revolution - photosynthesis
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Key events in life’s history
- Single-celled prokaryotes (in the ocean)
Similar to cyanobacteria - Oxygen revolution - photosynthesis
- The eukaryotic cell
How did the eukaryotes
evolve from their
prokaryotic ancestors?
Serial Endosymbiosis
Endosymbiosis Event 1
slide 24
MITOCHONDRIA
prokaryotic cell engulfed
a small cell that would
evolve into an organelle
found in all eukaryotes
Endosymbiosis Event 2
slide 25
PLASTID (like chloroplast)
A photosynthetic
bacteria was then
engulfed by the
heterotroph
Evidence supporting Endosymbiosis
- Inner membranes have enzymes and transport systems
that are homologous to those found in the plasma
membranes of living bacteria. - Replication: replicate by a splitting process that is similar to that of certain bacteria.
- DNA circular molecules not associated with histones
- Ribosomes - RNA sequences, and sensitivity to certain
antibiotics similar to bacterial ribosomes
slide 26
Key events in life’s history
- Single-celled prokaryotes (in the ocean)
Similar to cyanobacteria - Oxygen revolution - photosynthesis
- The single-celled eukaryotes
- The multicellular eukaryotic forms
● Algae and soft bodied animals
● Cambrian explosion - animal phyla appear
(sponges, cnidarians, molluscs) - Colonization of land (plants and fungi)
Summary of Key events in life’s history
slide 28
- What affects species diversity?
The rise and fall of groups:
* Differences in speciation and extinction rates
* Depends on speciation and extinction rates of its member species
* These changes are affected by processes
○ Plate tectonics
○ Mass extinction
○ Adaptive radiation
The Model of Biodiversity (S vs.E)
Speciation vs Extinction
- The arrows indicate the five
major mass extinction events. - Biological diversity increased
vastly since the Cambrian
period - Five major mass extinctions
have occurred in the distant
past - Permian period - 96% of all
species may have perished - Cretaceous extinction –
disappearance of dinosaurs
asteroid impact, perhaps causing global forest
fires and obscuring the Sun for months by
throwing particles into the air.
slide 30
Theory of plate tectonics
● Movements in the mantle cause the plates to
gradually shift in a process called continental drift
● Tectonic plates can drift apart, collide (forming mountains), or slide past each other (causing earthquakes)
slide 31-32
Consequence plate tectonics
● Alters habitats in which
organisms live
● Major Climate change
● Allopatric speciation
Species have 2 choices
* Adapt
* Face extinction
slide 33
Mass Extinctions
Extinct - species that has been permanently lost
* Simultaneous losses of many lineages
* 99% of all species that have ever lived are now extinct
Fossil records: more than 20 mass extinctions
Extinction can be caused by changes to a species’ biotic or abiotic environment
Mass extinctions occur when large numbers of
species rapidly become extinct worldwide
How speciation and extinction affect diversity
slide 35
Big 5 Mass extinctions events
- Triggered by disruptive global change
- Fossil record over the past 500 my - 5 mass extinctions
- More than half of all of marine species became extinct
in each event
slide 36
Big 5 Mass extinctions events
- Permian extinction - 252 mya (caused by volcanoes)
- Cretaceous extinction - 66 mya (dinosaur extinct)
slide 37
A sixth mass extinction is under way?
- The number of species in the world today > than
it has ever been - decreasing at an alarming rate due to human
activities - 1 /4 of all species may become extinct in the near future
endangered species
Endangered species
organism that is threatened by extinction
Major causes lead to 6th mass extinction
- Habitat loss,
- Introduced species
- Overharvesting
- Global climate is warming
slide 39-40
Adaptive Radiation
Rapid period of evolutionary change where
many new species arise and adapt to different ecological niches
Causes:
* The opening of niches following mass extinctions
* The evolution of novel characteristics that enable
the exploitation of new resources or habitats
* The colonization of new regions with few or weak
competitors
Adaptive Radiation - Mammals
- Prior to 66 million years ago, the size and
diversity of mammals was restricted by predation
and competition from dinosaurs - After the extinction of terrestrial dinosaurs,
mammals underwent an adaptive radiation
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