History Of Life Flashcards
Scientists estimate that the earth came into existence approximately
4,6 billion years ago
Scientists estimate that the earth came into existence approximately
4,6 billion years ago
Life on earth began
3,8 billion years ago 2ith a unicellular, prokaryotic cell similar to a bacterial cell. Multicellular cells developed a few billion years later.
Scientists try to make sense of history of life on earth by relating it to important events like
The increase in oxygen levels in the Earth’s atmosphere
Climate change like ice ages
Geological events like the continental drift
Fossil evidence
Increase in energy levels
When earth was formed, the oxygen levels were very low. Modern theories suggest that the first life forms ege the prokaryotes which appeared 3,8 billion years ago didn’t need oxygen. They respired anaerobically and therefore obtained energy from their food without using oxygen.
When different bacterias arose that could produce their own food through the process of photosynthesis, carbon dioxide which occurred in large quantities in the atmosphere was used which made and released oxygen. The increase in oxygen levels in the atmosphere resulted in an increased variety of living organisms of earth
Climate change
Iice ages are long Geological periods of drastic decrease in the temperature of the Earth’s surface and atmosphere.
Glaciation takes place because large ice sheets form due to the cooling temperatures
At least 4 ice ages occurred since the origin to earth.
During the ice ages many species that could not adapt to the low temperatures died out.
Some species were forced to migrate towards the equator where the temperatures were higher.
The climate was drier because most of the water was trapped in snow and ice. Many terrestrial species became extinct due to the dry climate.
Due to the ice formation the sea level dropped resulting in the decreased habitats and the extinction of many aquatic species.
Ice ages therefore affected life on earth due to the extinction and redistribution of species
Geological events
Up until 200 million years ago all continents were fused to form one giant continent, PANGAEA which broke into two super continents :LAURASIA IN THE NORTH AND GONDWANALAND IN THE SOUTH.
As a result of the continental drift the climate changed. Habitats also changed or were destroyed. A large number of life forms became extinct or had to adapt to the changing environment. By means of biogeography, evidence had been found that the continents wee once joined. Closely relate species occurring on different continents probably shared a common ancestor
Biogeography
Study of the distribution of existing and extinct plant and animal species in specific geographical regions on earth. Example :ostrich in Africa and emu in austand nandu in south America
Scientists claimed that flightless birds
May have been developed from a common ancestor and that when the birds were separated geographically when GONDWANALAND broke apart. The flightless birds probably adapted to the changing environment and new species developed.
Fossil evidence
Fossils are complete organisms or the remains, imprints or traces/tracks of organisms usually preserved in rock.
Remains of ancient life that has been preserved in rock.
Fosssils provide evidence of earlier life(extinct organisms) on earth and give information regarding the history of life on earth. Fossils also give indications of the climate and the environment of millions of years ago.
Examples of fossil evidence include the fossils of bivalve(mussel) and ammonite.
The study of plant and animal fossils is known as……. And a scientist who studies fossils is a….
Palaeontology
Palaeontologist
Bivalve
A marine/freshwater snail with a soft body that is compressed in a shell consisting of two separate parts that is joined with a strong flexible muscular hinge ege oysters.
Ammonite
An extinct marine snail with a flat spiral shell divided into chambers with wavy interlcoking walls and became extinct about 65mya
Trilobites (found in karoo)
Extinct arthropods, their bodies divided into horizontal segments and three vertical loves. Related to crabs and lobsters and became extinct 250 Mya.
Whale fossils discovered in
The Sahara desert.
