Grade 10 Life Science
History of Life on Earth
2 MYA
First forms of life First human
appears in the
oceans
4 Major Events in History
Increase in oxygen levels in the Earth’s
atmosphere
Climate change
Geological events
Fossil evidence
https://www.youtube.com/watch?v
=5Y0nYTHV4q4&t=320s
Increase in oxygen levels
• A major imbalance in atmospheric gasses existed (too
much CO2 and too little O2)
• Existing microorganisms were anaerobic (did not
require O2)
• Eventually aerobic, photosynthetic bacteria were
formed.
• Due to photosynthesis – more oxygen became
available and a greater variety of organisms began to
develop.
• Organisms use oxygen for CELLULAR RESPIRATION
(energy!)
Climate change
Definition: long term changes to the earths
temperatures and weather patterns.
• Climate change impacts the number of organisms on
earth and where they live!
Examples:
• Droughts
• Floods
• Global warming
• Ice age
The Ice Age
• The ICE AGE is an example of a major climate change event.
• Definition: A long term reduction to the Earth’s temperature
• Impacts of the ice age on Earth:
Glaciation sea levels dropped loss of habitats extinction.
Glaciation loss of available drinking water for land animals and loss of
vegetation (food source) extinction.
Lower temperatures animals that could not adapt became extinct.
Surviving organisms that could NOT ADAPT were forced to migrate toward
the equator (warmer climates)
Geological Events – Continental drift
• Definition: Events that cause changes to the structure or
the surface of the Earth.
• Continental drift: The movement of continents resulting
from the motion of tectonic plates.
Geological Events – Continental drift
https://www.youtube.com/watch?v=ALBUX31tW4M
https://www.youtube.com/watch?v=ryrXAGY1dmE
Evidence of continental drift
• Biogeography: The study of the distribution of exsiting and extinct
organisms in specific areas on Earth
• Shape of the continents (like a puzzle!)
• Closely related species found in different continents (biogeography)
Fossil Evidence for Rising Sea Levels
Fossils: A fossil is any preserved remains, impression, or trace of
any once-living thing from a past geological age.
Importance of fossils:
• Proof of prehistoric organisms.
• Indicates the type of climate and environment organisms lived
in.
Evidence of fossils of aquatic animals on land, suggests oceans
once covered the land.
Bivalves and Ammonites found in North
KZN
Trilobites in the Karoo
Whale fossils found in the Sahara desert
