LO 15:

Mass Extinction
Textbook:
EarthComm chapter 8 section 9
The Extinction of Species
• It is impossible to predict the success or failure of one species . Many
physical and biological factors interact in complicated ways , all these
factors determine the success or failure of a species.
• Also, the data from the fossil record seem to indicate that different
kinds of organisms have different rates of success.
• It is found that there are species that lasted for tens of millions of
years , others lasted for hundreds of million of years . Other life spans
for species only lasted for a few million years.
• The 2 main reasons for Extinction are loss of habitat and loss of
genetic variation
The Extinction of Species at the end of Mesozoic
• There was big difference in the landscapes of the Mesozoic Era and
the Cenozoic Era. (The terms come from the Greek meso-, meaning
middle and kainos-, meaning new.)
• The group of animals that dominated the Earth for nearly 130 million
years during Mesozoic suddenly became extinct , the extinction
process mostly took place almost overnight. This sudden extinction
affected some plants and many groups of animals that lived on land.
It affected much of the food web in the oceans as well.
• Groups from phytoplankton to top carnivorous disappeared from
fossil record , they were never be seen again except as a fossil
material.
• Phytoplankton are small photosynthetic organisms, mostly algae and
bacteria, found inhabiting aquatic ecosystem.
• Carnivorous are an organism that eats mostly meat, or the flesh of
animals, sometimes carnivores are called predators.
• The post boundary biosphere was very different in nature. It was
established early in the Paleogene. It took several million years for the
plant and animal groups known to exist now to evolve. It took a long
time to fill all the ecological spaces opened by this extinction event.
• The Paleogene is one of periods in tertiary period of Cenozoic Era.
• The post-boundary fossil record shows that changes in the kinds of
animals now extinct are linked to food source(s). They are related to
the appearance and disappearance of these food sources.
• The fossil record shows that when evolution comes and changes the make
up of plants in a community, dependent organisms must find a new food
source. They must change how they process food for nutrition as well. If
they are not able to do so, they face extinction.
• Until the Mid-Cenozoic, there was no evidence in the fossil record for
grazing animals. About this time grasslands appeared . Following this, many
new groups of animals are found for the first time in the fossil record. The
diets of these animals include the plants of the grasslands like grazing
animals .
• In North America, such animals include camels, rhinoceroses, and horses.
Also included are many other mammals that are now known to be extinct.
The extinction of a few species now and then appears to be a normal
phenomenon. Scientists refer to the appearance and disappearance of a
few species at any time as background extinction.
• Background extinction is normal extinction of species that occurs as a result
of changes in local environmental conditions.
Biodiversity & Mass Extinction
• It is the diversity of different biologic species and/or the genetic
variability among individuals within each species.
• Fossil record sometimes show a change in the biodiversity
• A mass extinction event is when species vanish much faster than they
are replaced. This is usually defined as about 75% of the world's
species being lost in a 'short' amount of geological time - less than 2.8
million years.
• The major types of diversities in the biodiversity are genetic diversity,
species diversity, ecological diversity and functional diversity
• There have been five major ones throughout the history of life. During
these, up to 90 percent of the known biodiversity was lost. One such event
took place at the end of the Palaeozoic Era. This was between the Permian
and the Triassic Periods.
• it was more devastating to life on Earth than extinction at the end of
Mesozoic.
• Geologic time is divided into the Palaeozoic, Mesozoic, and Cenozoic
Eras. The specific places the time is divided and the time each era last
has a reason. The reason is the size and abruptness of the extinctions.
Causes of Mass Extinction
• A scientist named Luis Alvarez and his colleagues proposed a
hypothesis. It stated that the extinction was caused by the collision of
a huge asteroid with Earth. They based this on studies of sections
through sedimentary rocks. These rocks were found at the Mesozoic–
Cenozoic boundary. In several sections, they found geochemical
evidence. Where amounts of element iridium in this time was many
times greater than normal amounts of the element iridium. The
evidence pointed toward a catastrophic collision.
• Iridium is very rare on Earth’s crust. Large amounts of
iridium are found on meteorites and comets. Therefore, the
iridium was introduced into the Earth system during certain
impacts.
Another Evidence of the collison
• Another important piece of evidence was found in the Yucatán
Peninsula of Mexico. It was the remnants of a colossal impact
structure. This structure is called the Chicxulub crater. The collision
placed so much dust and ash into the atmosphere that the climate
became much cooler. It is thought that light could not reach Earth’s
surface. Earth’s ecosystems were stressed for a long time after the
collision. This led to widespread extinction of many species. Evidence
of sediment movement and deposition by a gigantic sea wave could
be seen in the Gulf of Mexico. This evidence, likely caused by the
impact, has strengthened the hypothesis.
Another Evidence
• There is also good evidence for increased volcanic activity
around this time.
• A few scientists like an alternative hypothesis for the great
extinction. It has to do with climate change induced by the eruption
of the volcanoes. Evidence is still being gathered. There are still
details to resolve about the extinction and its causes.