Answer:
An asteroid impact.
Explanation:
An asteroid impact is considered to have tossed rubble across the earth, killing off many species of plants and animals, 65 million years ago. Volcanic activity is involved in at least four mass extinctions, whereas an asteroid in just one.
Answer:
Single-cell organisms
Explanation:
In 1735, Linnaeus introduced a classification system with only two kingdoms: animals and plants. Linnaeus published this system for naming, ranking, and classifying organisms in the book "Systema Naturae". In the epoch that Linnaeus created this system, single-cell organisms such as bacteria and protists were almost unknown. In 1866, E. Haeckel added a category including both bacteria and protozoa, thereby adding a category formed by single-cell organisms (different from animals and plants). During the 1900-1920 period, bacteria were classified as a separated kingdom named 'prokaryotes'. The current three-domain classification system was introduced by C. Woese in 1990. In this system, all forms of life are divided into three different domains: archaea, bacteria, and eukaryote domains (this last composed of protists, fungi, plants and animals).
Vitamin b12 is the most popular deficiency at the moment- B12 creates red blood cells which travels oxygen around the body- having B12 deficiency can lead to anaemia.
Genetic engineering:Pros: produces more food, makes organisms more fit, increases knowledge and knowledge is good.Cons: Some say it's: playing God, dangerous due to recombination of DNA, contamination of the gene pool, big pharma could take over the "means of production".
In-vitro fertilization: Pros: Allows people who couldn't have children to do so, increases knowledge and knowledge is good.Cons: Expensive (really expensive), can lead to overpopulation (minor), can be done irresponsibly (minor as everything can be).