Extinction is the result of animals or plants being unable
to adapt to changing conditions. In some cases, scientists have
identified the problem which resulted in the loss of an entire species.
More often, extinction is created by a complex interaction between
many problems, as in the case of the dinosaurs.
Extinction is the process in which groups of organisms (species)
die out. If the birth rate is less than the death rate over time,
extinction results. Extinction is a natural result of evolution.
Species go extinct when they are unable to adapt to changes in the
environment or compete effectively with other organisms. Well over
99 per cent of the species that have ever lived have gone extinct.
1. Extinction strikes in both the land and the sea.
2. On the land, while animals suffer repeatedly, plants tend to be highly
resistant to mass extinctions.
3. Preferential disappearance of tropical forms of life during mass
4. Tendency of certain groups of animals to experience them repeatedly
(for example, trilobites and ammonoids).
5. Alleged equal spacing, or periodicity in geological time (occurring
about every 26 million years). Credits
These similarities between distinct extinction occurrences
aid paleontologists in determining the agents the agents that
perpetuated the disappearances of species in each extinction
Such agents are currently divided into two types:
1. Catastrophic Agents- such as meteorite impacts and comet showers,
2. Earth Agents- such as volcanism, glaciation, variations in sea level,
global climatic changes, and changes in ocean levels of oxygen or salinity
Although these agents can explain mass extinction, the causes of mass
extinction events remains relatively unknown. Credits
Nemesis hypothesis of Raup and Sepkoski, theorizes that there
is a periodicity of 26 million years to mass extinctions which
is caused by collisions with comets from the Oort cloud as
they are perturbed in their orbits by a dark star (a companion
star to the sun). The search for the "Nemesis Oort cloud"
Major Extinction Events Overview
The five largest mass extinctions in Earth's history occurred
The late Ordovician period (about 438 million years ago) -
100 families extinct - more than half of the bryozoan and
brachiopod species extinct.
The late Devonian (about 360 mya) - 30% of animal families
At the end of the Permian period (about 245 mya) - Trilobites
go extinct. 50% of all animal families, 95% of all marine
species, and many trees die out.
The late Triassic (208 mya) - 35% of all animal families die
out. Most early dinosaur families went extinct, and most synapsids
died out (except for the mammals).
At the Cretaceous-Tertiary (K-T) boundary (about 65 mya) - about half of all life forms died out, including the dinosaurs, pterosaurs, plesiosaurs, mosasaurs, ammonites, many families of fishes, clams, snails, sponges, sea urchins and many others.
The Extinction of the Dinosaurs: Most dinosaur species
perished in background extinctions that occurred throughout their Mesozoic
Era. The other dinosaur species died out during the several mass extinctions
that occurred in the Mesozoic: at the end of the Triassic (213 million
years ago), during and at the end of the Jurassic (at 190, 160, 144
mya), and during and at the end of the Cretaceous (at 120, 82, and 65
Reports on new discoveries relating to dinosaurs; both current and archived
KT Event This series of web pages has been developed
by the Year IV MSci Geology students at the University
101 Crazy Theories about Dinosaur Extinctions
The pattern and timing of extinction
Evidence for Late Cretaceous Climatic Change: Isotopic
Gradual extinction and climate change
Timing and Rate of Other Extinctions; What else died
Evidence for Impact, 1980-1990
The Chicxulub Impact Site - Discovery and Effects
Impact Geology, Chemistry and Physics
Each page links to even more information. Good job!