Transcript Biodiversity through Earth history

Chapter 13
Biodiversity Through Earth History
The Fossil Record of Biodiversity
Underlying assumption is that the process of evolution is
occurring
• evolution: creation of new species
• random mutation: genetic changes
• natural selection: environmental pressures
favor certain characteristics
• adaptation: favored characteristics prevail
• extinction: death of all members of a species
The Fossil Record of Biodiversity
The text starts off with two ideas about how the number of species changes
over time that do not seem to pan out
One view is that, perhaps, diversity is a dynamic process:
logistic growth – “S-shaped” growth
observed for populations, common model used in population dynamics
rate of change in number = origination - extinction
of species on earth
rate
rate
This does not
seem to be the
case.
The Fossil Record of Biodiversity
These observations do not
appear to be logistic, but do
they indicate exponential
growth in # of species?
Problem with this: # of species
may simply be a function of the
amount of sediment available.
Does not appear to be either
logistic or exponential
The Fossil Record of Biodiversity
The taxonomic tree for
homo sapiens
The Fossil Record of Biodiversity
Data on the number of
new appearances of
marine invertebrates of a
given age (namely, as
they appeared) by phylaclasses-orders taxonomic
levels. Compare to
previous data - no
exponential growth is
observed when looking
at the evidence this way
The Fossil Record of Biodiversity
Marine invertebrate fossils indicating
diversity through geological time
At least five major extinctions over the
past 500 m. y.
Largest mass extinction at end of
Permian, 251 mya. Best researched
extinction (dinosaurs) is the CretaceousTertiary (K-T), 65 mya.
65 my
440 my
360 my
251 my
206 my
Fossil record indicates high taxonomic
levels are less affected, and that lower
taxonomic levels recover rapidly from
mass extinctions
Mass extinctions cause great losses but
stimulate origination.
The Cretaceous-Tertiary (K-T) Mass Extinction
(see chapter 1 also)
• Extinction of dinosaurs, many other
marine and terrestrial species (both
animal and plant)
• Iridium: normally deposited at a
slow, known, rate from
extraterrestrial sources. Iridium
concentrations in the layer at the K-T
boundary are so high that it could not
have been deposited by normal
deposition, must have been a
massive, sudden extraterrestrial
source.
• Most iridium on earth is in core,
concentration in asteroids are much
higher than on earth’s surface
The Cretaceous-Tertiary (K-T) Mass Extinction
(see chapter 1 also)
• Estimated size of meteorite, from
amount of iridium, = 10km diameter
• Example of a “shock” to the earth
system. The climate, biosphere,
recovered, but at different rates.
Biosphere “recovery” was very
different from prior biosphere.
The Cretaceous-Tertiary (K-T) Mass Extinction
What caused it, and how did the earth system respond?
This has been the most studied, and perhaps most controversial,
extinction event. Big debate in the scientific literature in the
1980s – 90s
Realistic possibilities:
• Sudden sea level or climate change
• Volcanic eruptions
• Meteorite (comet or asteroid, extraterrestrial) impact
The Cretaceous-Tertiary (K-T) Mass Extinction
Sudden sea level or climate change
Not likely, because some of the times of greatest climate and/or sea level
changes have not coincided with mass extinctions
Volcanic eruptions or extraterrestrial impacts
the idea is that the heat and explosion from the impact would kill everything
regionally, and that the subsequent cooling from dust / soot would kill many
things globally. Volcanic eruptions could result in global cooling from sulfur
aerosols in the stratosphere.
Impact would also send hot particles across the globe starting fires; destroy
the ozone layer for several years; caused tsunamis; food would be scarce for
survivors; CO2 would have been released increasing temperatures for
thousands of years; toxics across the globe; slow recovery time of biosphere.
The Cretaceous-Tertiary (K-T) Mass Extinction
Meteorite impact theory
Luis Alvarez’s 13 predictions which indicate that the geological evidence is
consistent with the meteorite impact theory (only some listed here)
•
Iridium layer should be at the
K-T boundary worldwide
•
Frequency of large meteorites
is sufficient to explain
the record
frequency of collisions of large objects with Earth.
The Cretaceous-Tertiary (K-T) Mass Extinction
Meteorite impact theory
Luis Alvarez’s 13 predictions that show that the geological evidence is
consistent with the meteorite impact theory
•Both plants and animals
should have been affected
•clays in the iridium layer
should be identical
worldwide, be different
than the layers above
and below, and have
an extraterrestrial
signature
Evidence for mass extinction of plants
The Cretaceous-Tertiary (K-T) Mass Extinction
Meteorite impact theory
Luis Alvarez’s 13 predictions that show that the geological evidence is
consistent with the meteorite impact theory
•There should be evidence
of high temperature and
high pressure at impact.
Sphericals (from cooling
of molten droplets in air)
and shocked quartz (only
forms when quarts is under
high pressure) are there.
•Evidence of wildfires
•Layer should be between a
change in fossils
Evidence for mass extinction of plants
The Cretaceous-Tertiary (K-T) Mass Extinction
Meteorite impact theory
Luis Alvarez says that the geological evidence is inconsistent with the
volcano theory
• Volcanoes would not
distribute the spherules
globally
• Shocked quartz has never
been found in volcanic
deposits, but is often found
in meteorite impact craters
• Volcanic deposits tend to have
low iridium concentrations
Evidence for mass extinction of plants
The Cretaceous-Tertiary (K-T) Mass Extinction
Location of the Chicxulub impact crater
Meteorite impact theory
Additional evidence:
• Helium isotopes found in
the layer are extraterrestrial
• The Chicxulub Crater:
- associated with cenotes
- contain spherules and shocked quartz
- enriched in iridium
- in the right age range
Size of impact crater
The Cretaceous-Tertiary (K-T) Mass Extinction
Did the biological pump shut down for
hundreds of thousands of years?
Currently, and prior to K-T, there is a
difference in C13/C12 ~2o/oo
Difference is caused by the biological
pump, algae preferentially take up C12,
then sink to bottom and decompose
After K-T, much smaller difference.
Extraterrestrial influences and extinctions
Asteroids: rocky material composed of minerals and metals
from dust to 100km in size
found mostly in the asteroid belt (between Mars and Jupiter)
Comets: materials that are volatile on earth but solid in space,
plus some minerals and metals
found mostly in the Oort Cloud
Extraterrestrial influences and extinctions
Both asteroids and comets can be deflected, by collision, into different orbits that
might cause them to collide with a planet, including earth.
Jupiter acts as a major gravitational attraction to deflected asteroids, affecting
their paths and possibly sending them towards other planets
Extraterrestrial influences and extinctions
Is there a 26 million year periodicity in the extinction record?
4 possible explanations:
1.
Galactic plane hypothesis
2.
Companion star hypothesis
3.
Planet X hypothesis
4.
Artifact of the way the
data are collected
Vertical lines drawn every 26 million years
Location of the Chicxulub
impact crater
Support for
meteorite
impact as a
cause for the
K-T mass
extinction:
frequency of
collisions of
large objects
with Earth.
Size of impact crater
Evidence
supporting
meteorite
impact and its
effect on plants
at the K-T
boundary
Extraterrestrial influences and extinctions
Is there a 26 million year periodicity in the extinction record?
4 possible explanations:
1.
Galactic plane hypothesis: our solar system moves up and down in a
26 million year cycle through the plane of the galaxy. When we pass
through the center, we encounter more gas/dust, higher chance of
disturbing the orbit of an asteroid or comet
Extraterrestrial influences and extinctions
Is there a 26 million year periodicity in the extinction record?
4 possible explanations:
1.
2.
Companion star hypothesis: our sun has a companion star (small brown
dwarf, <.08 size of sun) in an orbit that passes through the Oort cloud every
26 million years
Extraterrestrial influences and extinctions
Is there a 26 million year periodicity in the extinction record?
4 possible explanations:
1.
2.
3.
Planet X hypothesis: there is
a planet that we have never seen,
located in an orbit beyond Pluto,
that disturbs the Kuiper Belt
Extraterrestrial influences and extinctions
Is there a 26 million year periodicity in the extinction record?
4 possible explanations:
1.
2.
3.
4.
Artifact of the way the
data are collected:
data are collected in
stages, perhaps this
results in some funny
cyclicity in the data
Vertical lines drawn every 26 million years