Question

Compare and contrast mass extinctions and background extinctions. How do their size and geographic and taxonomic extent differ? Which one is often followed by adaptive radiation? Why? Include an example.

Answer 1

The extinctions are compared and contrasted as follows:

A. Background extinction- It is referred to as the usual or normal extinction rate.

1. Some species are present on Earth that cannot be sustain and survive. Such species get extent this type of simple extinction.

2. How often an extinction occurs naturally is a measure of background extinction.

3. There are 3 ways to measure background extinction. These include examining the number of species extinct over a period of time, estimating extinction rate over million years and looking over species survival rate over time.

4. Causes include normal changes such as environmental change or poor adaptation. Competition or predation also cause background extinction.

B. Mass extinction- A widespread event that is responsible for wiping out a majority living plants as well as animals which roughly makes about 50% of the total population is referred to as mass extinction.

1. The extinction of dinosaurs as a result of collision of an asteroid with Earth as per many scientists is an example of mass extinction.

2. Since the time that the Earth we know today came into existence around 98% of the species have gone extinct till now. This is due to mass extinction. Most of our current knowledge on various species is a result of study of fossils.

3. There have been around 5 mass extinctions that have taken place till now on Earth.

4. The causes of mass extinction are sudden, extraordinary and temporary environmental changes. Such rapid changes are a regression in sea level or plate tectonics or asteroid impact etc.