History of Life Flashcards
History of Life
Understanding the History of Life
Scientists use evidence, such as fossils, and deductive reasoning to understand the history of life.
Origin of Life on Earth
Earth is estimated to be over 5 billion years old.
Life on Earth is believed to have started 4 billion years ago.
Fossils, found mainly in sedimentary rock, provide evidence of past life.
Palaeontology is the study of fossils, and paleontologists are scientists who study fossil evidence.
Fossils
Fossils are the hardened remains of dead organisms.
Fossilization process involves the organism being buried by sediment, minerals replacing living tissue, and time and pressure turning the sediment into rock.
Erosion can expose fossils. If the organism is washed away, eaten, or rots, no fossil is formed.
Importance of Fossils
Identifying past organisms and environmental changes.
Understanding how organisms have evolved.
Aiding in mineral exploration.
Types of Fossils
Body Fossils: Fossils of the entire organism (e.g., bones, shells).
Mold and Cast Fossils: Mold is a hollow impression, while a cast is a solid mineral deposit filling a mold.
Trace Fossils: Tracks left behind by an organism (e.g., footprints, coprolites).
Fossils in Amber: Organisms trapped in hardened tree sap (amber).
Frozen Fossils: Organisms preserved in ice.
Petrified Fossils: Fossils where minerals replace all or part of an organism.
Methods to Date Fossils
Relative Dating: Determines the relative age based on rock layers (older layers are deeper).
Radioactive Dating: Uses radioactive elements to determine the actual age based on radioactive decay and half-life.
Example: When 50% of carbon 14 remains, the fossil is approximately 5700 years old.
Life Forms – Past/Present
Coelacanth: Fish that evolved 390 million years ago, once thought to be extinct.
Archaeopteryx: Prehistoric bird, a link between dinosaurs and birds.
Fossils in South Africa
South Africa contains the oldest proof of life on Earth, multicellular organisms, primitive land plants, ancestors of dinosaurs, origins of mammals and record of the origin of mankind.
Geological Timeline
Graphical representation dividing Earth's history based on life forms during specific times.
Includes eons, eras, and periods (e.g., Precambrian, Paleozoic, Mesozoic, Cenozoic).
Geological Time Scale
Divides Earth’s history from 543 million years ago to the present into Paleozoic, Mesozoic, and Cenozoic eras.
Precambrian period was 4600 – 570 mya.
Cambrian Explosion
Occurred between 544 and 505 million years ago.
Development of multicellular animals and hard structures.
Possibly due to higher oxygen levels.
Factors Influencing Change and Extinction
Climate Change: Ice ages leading to species extinctions and survival.
Oxygen and Carbon Dioxide Levels: Photosynthesis by bacteria increased oxygen levels.
Geological Events: Continental drift leading to competition and volcanic eruptions.
Continental Drift/Plate Tectonics
Formation of continents.
Caused competition, abiotic changes, and volcanic eruptions.
Contributed to mass extinction at the end of the Permian era.
Mass Extinctions
Periods when most life on Earth died out due to environmental disasters or failure to adapt.
5 major extinctions occurred where more than 50% of all species were killed.
Possible Causes of Mass Extinctions
Changes in sea levels altering salt and oxygen concentration.
Meteorite impacts and volcanic activities.
Global warming and ice ages.
Climate Changes
Cooling: Formation of glaciers, dropping ocean levels, decreased oxygen, and increased salt content.
Heating: Warmer climate leading to changes in food chains.
Volcanoes
Likely cause of the end-Permian extinction.
Ash and dust block sunlight, cooling the Earth.
Sulphur dioxide causes acid rain and the greenhouse effect.
Continental Drift/Tectonic Plates
Pangea divided into Laurasia and Gondwana.
Proposed by Alfred Wegner.
Meteorites/Asteroid Collision
A meteorite crash 65 million years ago may have led to the extinction of the dinosaurs.
Debris blocked sunlight, decreasing photosynthesis and oxygen levels.
Evidence in South Africa
Vredefort dome is a crater caused by a meteorite.
The Sixth Extinction
Currently occurring, caused by human activities.
Causes include invasive species, spread of disease, pollution, depletion of resources, increased temperatures, and habitat destruction.
Causes cont.
Overexploitation, pollution, climate change, land use change.
Globalization, ocean acidification, altered water flow, and land degradation.