Everything Life Sciences Grade 10

Figure 11.13:

Phillip Tobias,

South African anti-

apartheid activist,

world-famous

palaeoanthropolo-

gist.

FACT

The Golden Toad of

Costa Rica has been

extinct since around

1989. Its
      disappearance has
      been attributed to a
      confluence of
      several
      factors,including
      global warming
      event known as El
      Nino, fungus, and
      the introduction of
      new species that
      out-competed it for
      habitat and food.

Major mass extinction

event

Date of occurrence Major events

Cretaceous-Paleogene

extinction event

65 million years ago Approximately 75% of all

species became extinct.

Mammals and birds

emerged as the dominant

land vertebrates

Triassic-Jurassic event 205 million years ago Most non-dinosaur

species were eliminated,

leaving land dinosaurs

with no competition

Permian-Triassic event 250 million years ago This was Earth’s largest

extinction event. Almost

all marine life, 70% of

land species and over

80% of all marine genera

were eliminated. The

event had great

evolutionary significance

because it allowed the

vacant habitats and

ecosystems to be filled by

new species through

natural selection.

Late Devonian extinction 375–360 million years

ago

This was a prolonged

period of extinction

lasting up to 20 million

years. During this period

up to 70% of living

species were eliminated.

Ordovician-Silurian

extinction event

450–440 million years

ago

Over 50% of all genera

were eliminated during

this period and is ranked

as the second largest

mass extinction in Earth’s

history

Ongoingsixth mass extinction DUMMY

• We are currently living through the ’sixth’ mass extinction according to many scientists.
  The present rate of extinction of species is thought to be 140 000 species per year since
  approximately 10 000 BC and has continued into the 21st century.


• The extinction includes disappearance of large mammals such as the woolly mam-
  moth.


• The sixth extinction event is thought to be occurring at a rapidly increasing rate.


• The two major causes for the sixth extinction are thought to be human hunting and
  the rapid rise in human population. You will learn more about the impact of human
  activity on the environment in Grades 11 and 12.

Chapter 11. History of Life on Earth 331