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.

Abiogenesis and Panspermia

The abiogenesis theory states that life came originated from simple organic compounds that were created on the earth from the pre-biotic soup that existed. However on the other hand, the panspermia theory states that life on Earth originated from comets and asteroids carrying bacterial life from the universe.

The Urey-Miller experiment provides support that the occurrence of abiogenesis is possible. The Urey-Miller experiment aimed to create organic compounds via a system that simulated similar conditions of pre-biotic Earth. The simulation consisted of a recirculating system with heated water (as the ocean), a chamber with electrical charges (as the atmosphere with lightning), and a condenser for gases in the 'atmosphere 'chamber to dissolve in the water. These chambers consisted of ammonia, nitrogen, methane, hydrogen gas, and carbon dioxide. After a while, the experiment's result showed simple organic molecules in the 'atmosphere' chamber, whereas amino acids and other organic acids were found in the 'ocean' chamber.

However, it is still possible for the panspermia to be valid because abiogenesis may have occurred on a different planet and comets may have transported the products to Earth while abiogenesis was occurring on Earth.

Scientists think the RNA replication or metabolism occurred first before protobiont cells began to form in micro environments for many reasons.

Scientists think RNA replication occurred first because RNA have the ability to replicate themselves as well as catalyzing reactions. RNA also have the ability to attract and link amino acids into proteins, which are the building blocks of life. Furthermore, scientists believe that RNA were able to persist because of the clay from volcanic ashes would cover it from harmful UV rays.

Scientists also argue that metabolism occurred before the protobiont cells began to form because they believe that the Earth may have started out with the first living thing on Earth as a primitive metabolic life sustaining itself with a series of reactions with CO2 or CO catalyzed by metal sulfide.

Protobionts are thought to be precursors to prokaryotic cells. They consist of abiotically produced organic molecules surrounded by a membrane like structure. Protobionts have characteristics that are related with life such as simple reproduction, metabolism, excitability, and the maintenance of itself to survive in its environment (with the help of its membrane). Due to this, many scientists believe RNA replication and metabolism occurred before protobiont cells began to form. RNA is needed for the protobiont cells to execute simple reproduction and metabolism is needed so it can energize itself to survive. 

However, whether RNA replication or metabolism may have been the very first occurrences of life, both the abiogenesis and panspermia theories still have validity because organic compounds could have still been created on Earth or survived on a comet traveling to Earth to create protobiont cells.