Question

Number of known species of organisms on this earth is -
a. 5 million
b. 3.2 million
c. 1.7 million
d. 1.32 million

Answer 1

Earth is defined as the whole variability of life forms. More than 99 percent of all species that ever lived on Earth are believed to be extinct. Approximations on the number of Earth's existing species range from 2 million to ${10^{12}}$, of which about numerous species have been recorded thus far and over 80 percent have not yet been described.

Complete answer:
Great biodiversity subsists on our planet. Millions of living plants and animal species are blooming on Earth. An approximate of 1.7 million organisms are known to exist. New species are getting discovered and recorded every year.

Global biodiversity is deteriorated by extinction and speciation. The background disappearance rate varies amid taxa but it is calculated that there is around one extinction per million species years. Mammal species characteristically persist for 1 million years. Biodiversity has developed and shrunk in the earth's past due to abiotic factors such as extinction events caused by geographically rapid changes in climate. Climate change 299 million years ago was one such occasion. Cooling and drying resulted in a disastrous rainforest collapse and consequently a great loss of diversity, mainly of amphibians.

Hence, the correct answer is option (C).

Note: Biodiversity is typically plotted as the richness of a geographic area, with some reference to a temporal scale. Types of biodiversity involve taxonomic or species, environmental, morphological, and genetic diversity. Taxonomic diversity, which is the figure of species, genera, family is the most commonly assessed type. A few studies have attempted to quantitatively illuminate the relationship between dissimilar types of diversity.