GeologyRocks

What is A Mass-Extinction?

What Is A Mass-Extinction?

An extinction event is defined as a sharp decrease in the number of species over a short period of time. A mass extinction is further defined based on four points, pattern, duration, breadth and magnitude, and the event must:

• be confined to a short period of geological time
• Affect a wide variety of clades, that occupy a wide range of Habitats
• And eradicate a high proportion of species.

Foraminiferans As Palaeoenvironmental Indicators.

Foraminiferans (hereafter referred to as Forams) are unicellular protists that inhabit the world’s oceans and range from 20µm to a few centimetres in size. They tolerate a wide range of salinities from esturine to fully oceanic (~ 35‰) but are NOT found in freshwater. They can be either planktonic or benthic, do not photosynthesise so inhabit various depths, and are active predators.

The Use Of Diatoms As Palaeoenvironmental Indicators

Diatoms are microscopic, photosynthetic algae (which due to the yellow-brown chloroplasts they contain are sometimes referred to as golden algae). Comprising one of the most common types of phytoplankton, they are found in a diverse range of environments from freshwater to saline oceanic waters. It is estimated that 20-25% of all the organic carbon fixation on Earth; via photosynthesis, is attributable to diatoms - in large due to their great abundance.

The Origin and Early Evolution of Birds

Birds are phylogenetically considered to be members of the theropod dinosaurs; their closest non-avian relatives are the dromaeosaurid theropods. The first known fossil bird is Archaeopteryx, from the late Jurassic of Bavaria, Germany, which is represented by seven skeletons and a feather. There is no fossil evidence from before this time that has been proven to be of avian origin. The fossil record of modern birds began in the early Tertiary (Padian et al., 1998).

What kinds of isolation can lead to the formation of a new species?

According to the biological species concept, populations are different species if gene flow between them is prevented by biological differences, known as reproductive barriers. If populations exchange genes they are conspecific, i.e. belong to the species, even if they differ greatly in morphology. If they are reproductively isolated, they are different species even if they are indistinguishable phenotypically. Therefore speciation arises from the evolution of biological barriers to gene flow (Futuyma, 1998).