- Radioactive isotopes can be used to approximate the age of certain materials. Certain isotopes such as Uranium-238, Potassium-40 and Carbon-14 have an unique rate of decay that can be measured by scientists. Each of these radioactive isotopes have a specific half life where after a certain period of time, half of their molecules will have decayed into their stable daughter isotope.
- Half-life: time required for half of the radioactive molecules to decay
- Radiocarbon Dating: All organisms have carbon, that while alive, is found as a mixture of carbon-12(stable) and carbon-14(radioactive). After death, the carbon-14 will slowly decay because it can no longer be replaced by the environment. After 5730 years, half of the carbon-14 would be gone. The amount of carbon-14 left will determine the approximate age of the sample. The half-life of carbon is fairly small so samples are only limited up to an age of about 60,000 years before all the carbon-14 is gone
- Potassium-Argon Dating: is used for dating igneous rocks so that the approximate age of a fossil can be predicted by dating the rocks around it. Potassium 40 is released by lava from volcanoes and will decay into argon-40. It has a half life of 1,300 million years. By determining the time when the volcano erupted, the age of the rock can be traced back using potassium-40.
Human evolution
The fossil record can help illustrate the physicll appearance of humans over time. It will tell us
Major Anatomical features similar to primates:
- Binocular Vision: eyes face forward
- Large Brain
- Opposable thumbs capable of grip
- Nails, lack of claws
- Touch pads on each digit
- Skull adapted for upright posture, tendency to sit upright as well
- Long limbs that rotate freely at the hips or shoulders
- Characteristics such as emotions, motor coordination, memory, thought, education, processing of sound, colour vision
- Childcare
Hominid: Lineage of humans
The hominin fossils have some similarities or trends that seem to occur in all the fossils founds
- General S shape of spine (posture similarities), shows the increasingly upright posture over time
- Length of limbs changing sizes as walking on two legs becomes more common
- Flatter faces
- Teeth getting smaller and V shaped jaws to reflect diet changes
- Reduced body hair caused by technological and cultural changes (invention of clothes)
- Emphasis on different muscle groups (leg muscles, less arm muscles)
Although there are thousands of fossils, there are still many gaps causing some uncertainties regarding human evolution
Incomplete fossil record
- Fossils are hard to create and rarely occurs. Requires specific conditions in order for something to fossilize
- Many organisms will decompose before they can fossilize
- Fossilization usually occurs to dense parts that can be destroyed by weather
- Certain independent fossils might not be enough to prove a species existed as they might have been a genetic mutation
- Few complete fossils of humans have been discovered, usually only parts
- Limited fossil data are re-interpreted with the help of new technologies or theories
Correlation between diet change and the increase in brain size:
- Changes in habitat might have influenced diet. More meat will increase skull capacity and brain size. The diet also provides more energy to aid the brain function and learning capability. This may result in better cognitive skills such as hunting and cooking and a improved diet.
Genetic Evolution vs. Cultural Evolution:
Genetic evolution sees changes in the genes due to inheritance and the transfer of genes across generations. Cultural evolution is the passing on of ideas and information across generations. Both of these types of evolution can benefit humans by passing on genes that improve/maintain the culture or by maintaining/improving the genes that are inherited. Changes in culture can also alter the genetics for example pollution that can cause mutations in the genes or medicine that can remove the need for genetic evolution.
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