Hominid Evolution and Carbon Dating

Hominid Evolution

Ardipithecus ramidus (4.4 million years ago)

-divergent large toe with a rigid foot

-pelvis tree climbing and bipedal activity

-ape ancestor not chimpanzee like

-canine teeth = same size male and female

-wooded environment

-3 ft 11 in, 110 lbs

Australopithecus afarensis (2.95-3.85 million years ago)

-ape and human characteristics

-apelike features:

face proportions 

braincase (small brain)

strong arms with curved fingers (climbing trees)

-human features:

small canine teeth

body stood on two legs

-could live on trees and ground

-males (4ft 11in, 92 lbs)

-females (3ft 5in, 64 lbs)

Australopithecus africanus (2.1-3.3 million years ago)

-rounder cranium w/ larger brain and smaller teeth

-apelike:

long arms

sloping face that juts out (pronounced jaw)

-pelvis, femur, footbones: walked bipedally

-shoulder and hand: climbing

-males (4ft 6in, 90 lbs)

-females (3ft 9in, 66 lbs)

Homo habilis (1.4-2.4 million years ago)

-larger braincase

-smaller face and teeth

-ape like features: long arms & prognathic face

-average (3ft 4in- 4ft 5in, 70 lbs)

Homo erectus (143k-1.89mil years ago)

-more adapted to the ground

shorter arms

long legs

=walk and run more

-average (4ft 9in - 6ft 1in, 88 - 150lbs)

Homo neanderthalensis (28-200 thousand years ago

-closest extinct human relative

-skull features

large middle part of face

angle cheek bones

huge nose for different air (humidifying and warming)

-shorter stockier bodies (cold environments)

-brain same size sometimes larger

males (5ft 5in, 143 lbs)

females (5ft 1in, 119lbs)

Homo sapiens (200,000 to present)

-large brains

-thin walled high vaulted skull

-flat almost vertical forehead

-smaller teeth

Summary

-The braincase gets larger incrementally

-Generally get taller and heavier

-Shorter arms and longer legs

-Nose smaller

-Smaller teeth

-Became only bipedal

-These traits are meant to suit us to live on the ground

http://humanorigins.si.edu/resources/intro-human-evolution

Carbon dating

Carbon dating is used to determine the age of fossils and requires the use of the radioactive isotope carbon-14. Carbon-14 is produced by cosmic ray protons which blast nuclei in the upper atmosphere, thus producing neutrons and bombard nitrogen creating carbon-14. This occurs at a rate which is constant, therefore we can use radioactive emissions of once-living matter and compare it to living ones. The results allows us to make a measurement of the time that passed.

Radioactive half-life is the time for half the radioactive nuclei to go through radioactive decay. Unstable radioisotopes decay into more stable forms (C-14 decays to C-12, which is stable.) 

Living organisms constantly exchange carbon with the atmosphere in the form of CO2; this results with the organisms to have nearly the same ratio of C-14 to C-12 with the atmosphere. However when the organism dies, it beings to undergo radioactive decay in which C-14 decays into a more stable C-14. This can be used to measure the amount of time an organism had been dead for.

Carbon dating is used for younger fossils because of the difference in half-life.

C-14 has a half-life of 5700 years which is useful for fossils that are 1000 to 10000 years old, whereas potassium (K40) has a half life of around 1.3 billion years therefore allowing it to be used for much older fossils.