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.
Geological timescale
The purpose of it is to represent a time line of life on earth from the origin of the earth. Time units are divided according to the age of the fossils that have been discovered. The largest defined unit of time is the aeon divided into 3 eras: palaeozoic, mesozoic and cenozoic. And each for these is further divided into periods:quaternary, tertiary and cretaceous.
Fossil record
Alll the fossils of different ages that have been discovered by palaeontologists are listed. However they are incomplete and don’t have an indication of all the organisms that lives a particular period.
Archaeopteryx
Transitional fossil known as the earliest and primitive bird displaying both characteristics of a bird and reptile.
Characteristics of reptiles
Sharp teeth in sockets
Finger with claws.
Long bony tail
Characteristics of bird
Feathers
Wihs bond for attachment of muscles for flight.
Marine fossils
Fossils found in the ocean
Glaciers
Large masses of ice.
Anaerobic
Respiration that occurs in the absence of oxygen.
The three main Eras of Earths history. dividing the geological time scale
Paleozoic, Mesozoic and Caenozoic
continental drift –
the theory that the continents were once all joined together and have slowly moved apart over millions of years.
convection currents
Circular currents in the mantle created by the rising of hot magma and sinking of cool magma. These currents cause tectonic plates to move.
crust –
The thin, rocky, outer layer of the Earth.
seafloor spreading –
The movement of two oceanic plates away from each other, which results in the formation of new oceanic crust and a mid-ocean ridge.
what causes extinction
The environment changes (eg. climate warms up)
A competitor moves into the habitat and takes food / nesting sites.
A predator moves into the habitat
diseases
Another plant or animal in the food web becomes extinct.
The British naturalist Charles Darwin (1809–1882) later suggested a more persuasive argument for evolution.
Darwin proposed that evolution took place through natural and sexual selection.
Darwin developed his theory of evolution after noticing
close similarities between certain fossils and the adaptations of modern day animals he saw during his round-the-world voyage on the HMS Beagle.
However, when Darwin learned that another British naturalist,
Alfred Russel Wallace, had proposed an almost identical theory of natural selection, he published his findings.
evolution
The development of new species as a result of natural selection.
extinction
The complete disappearance of a species due to changes in its environment that reduce its ability to survive and reproduce.
fossil
The preserved remains, impressions or traces of an organism that lived millions of years ago
natural selection –
The process where individuals that are well adapted to their environment survive and reproduce at the expense of less well-adapted individuals.
trait
A distinguishing and inheritable characteristic of an organism.
variation
The natural differences between individual members of a species.
he formed the theory that
organisms evolve to adapt to their environment and organisms with adaptive features allows survival and reproduction of the species that will live while the others die out
What happens when habitats change?
Adaptive evolution ensures that individuals within a species have traits allowing them to survive and reproduce in their habitat.
if the habitat changes, however, successful traits can become a disadvantage.Individuals that fail to reproduce, compete effectively for food or survive against new predators will eventually die out. If the last individual of a species dies, the species is extinct.
why did the dodo become extinct
The dodo was a large flightless bird that lived on the island of Mauritius.
It nested on the ground in forests, producing one egg at a time.When human settlers arrived on the island in the mid-1600s, they brought animals such as rats and dogs to the island, which ate the dodos’ eggs.The settlers chopped down the forests in which the dodos lived, and may have even hunted the dodo for food.
what could have hepled dodo survive
The dodo’s large size and inability to fly were adaptations that allowed this bird to survive
purpose of geological timescale
represent a timeline of life on earth from the origin of earth
What is the theory of plate tectonics?
he explanation for how the continents move came from observations of seafloor spreading and other effects. In 1967, these ideas were linked in the theory of plate the Earth’s crust is like a jigsaw puzzle made up of giant sections called tectonic plates.
These plates ‘float’ on top of the mantle and so can move around the Earth’s surface.
pangea
