history of life

• before an increase in oxygen levels 


  Earth's atmosphere did not have much oxygen it was first filled with carbon dioxide, nitrogen, and water vapour. The first life forms were single-celled organisms that did not need oxygen to survive they were called anaerobic. They obtained energy by breaking down organic compounds in their environment.
• increase in oxygen levels

  Around 2.5 million years ago a bacteria called cyanobacteria evolved the ability to perform photosynthesis. This was not good news for many existing life forms because oxygen was toxic to many organisms at that time. Aerobic organisms are organisms that require oxygen for their survival. As oxygen levels began to rise more it led to the diversification and complexity of life on Earth and multicellular organisms developed
• cooling of the earth


  Ice ages are long periods of time where Earth experienced extremely cold weather. During ice ages, large sheets of ice called glaciers are formed. Glaciation and the sudden cooling that it brought caused a large-scale of extinction of life forms. Scientists think continental drift and plate tectonics were responsible for glaciation.
• continental drift


  all the continents were one big land mass called Pangea. The super continents began to break up about 225-200 million years ago into large masses called Laurasia northern hemisphere and Gondwanaland southern hemisphere. According to this theory, Antarctica was once closer to the equator with a temperate climate as this land mass drifted towards the south pole it caused rapid cooling and the formation of glaciers.
• Biogeography


  refers to the study of past and present distribution of individual species.
• Theory of plate tectonics


  according to the theory of plate tectonics, the Earth is made from about a dozen large plates which fit together like a jig-saw puzzle.
• Fossil evidence


  Fossils are remains are ancient life forms preserved in rocks. Paleontology is the study of fossils. The presence of marine fossils in parts of the earth in which fossils were found for example Kwa-Zulu Natal indicates that these places were once covered in water.
• eons

  longest time periods and are hundreds of millions of years long. The phanerozoic eon is the most recent eon and it began 500 million years ago.
• Eras 


  The Phanerozoic eon is divided into three eras, the Cenozoic, Mesozoic, and the Paleozoic eras
• Periods 


  The Paleozoic is sub-divided into Permian, Carboniferous, Devonian, Silurian, Ordovician and Cambrian periods
• Archaeopteryx

  a transition fossil that has both reptile and bird features
• Cambrian explosion


  short period of time marking the origins of early origins of life forms. It is when there was a sudden appearance of major groups of animals
• The Cambrian period began about 543 million years ago and ended 505 million years ago it lasted 38 million years
• Mass extinction 


  Ordovician [444 million years ago] caused by climate change many trilobites became extinct
• Devonian [383-359mya]


  ice ages global cooling, glaciations almost all life forms died out
• Permian [252 mya]


  caused by many volcanic eruptions many frogs died out
• Triassic [201 mya]


  caused by acid rain and drop in oxygen in water causing many life forms to die out
• Cretaceous [66mya]


  all dinosaurs died out because of an asteroid and dust clouds from volcanic eruptions blocking out the sun
• Fossil


  remains of an organism that existed long ago and is preserved into a rock
• the Earth is over 5 billion years old
• history of life on earth started 3500 million years ago
• human history only stretches about 10 000 years back
• the first modern humans appeared between 50 000 and 100 000 years ago
• Paleontologist


  person that studies fossils
• Petrification

  process where an organism is replaced with silica or calcium and turned into stone
• Sedimentary rock

  rocks formed in sand, mud, or carbonate in a river
• Relative dating

  age of a fossil is worked out by trying to find out how it is related to another fossil or geological events
• Radiometric dating

  finding the age of fossils using radioactive substances
• continental drift

  continental drift theory is what scientists use to explain the formation of glaciers during ice ages
• Biogeography


  study of past and present distribution of individual species
• Oparin-Haldane Hypothesis


  A scientific hypothesis that proposes a naturalistic explanation for the origin of life on Earth, involving the formation of the early Earth, the primordial soup, simple cells, and the emergence of life.
• Simple Cells


  The first replicating and evolving organisms, formed from the combination of simple organic compounds in the primordial soup.
• Evidence for Continental Drift

  Includes the fit of the continents, the presence of similar rock formations and fossils on different continents, and the distribution of ancient climates and magnetic fields.
• Supercontinent Pangea


  A single supercontinent that formed around 300 million years ago, when all of the Earth's continents were joined together. Pangea later broke apart, forming the continents we know today.
• Impact of Continental Drift

  Has had a significant impact on the Earth's climate, geography, and biosphere, including the formation of mountain ranges, the creation of new habitats for life, and the separation of species into different populations.
• The atmosphere in primitive Earth had little to no oxygen
• The absence of oxygen allowed the gases present in the atmosphere at the time to form organic molecules such as fatty acids and proteins which were building blocks of living organisms
• The first life forms [prokaryotes] which developed about 3.5 billion years ago did not need oxygen to survive they are anaerobic
• Between 3.5-2.5 million years ago


  1. Different bacteria began to develop called cyanobacteria

  2. Cyanobacteria were able to manufacture food by the use of photosynthesis
• As more and more oxygen filled up the earth's atmosphere organisms that needed oxygen to produce food/survive developed these are called aerobic