First of all it is important to understand the history of life on earth in it's most simplest form -
Precambrian Era - 4600-1000 million years ago
- Origin of solar system and Earth.
Paleozoic Era - 544-245 million years ago
- Primitive marine algae flourish and the first fishes appear.
Mesozoic Era - 245 - 65 million years ago
- In 245-208 million years ago, First mammals and dinosaurs appear.
- Mass extinction of marine life, and some terrestrial life including the last dinosaurs happened between 146-65 million years ago.
Cenozoic Era - 65 million years ago - Present
- Widespread flourishing of birds, mammals, insects, and flowering plants.
- Evolution of genus Homo
happened 2.5 million years ago.
The beginning of our planet:
When Earth first formed around 4.5 billion years ago a multitude of meteorites smashed into the forming planet, and the kinetic energy of these
extraterrestrial rocks was converted into heat on impact. Still more heat was released by the decay of radioactive atoms. The rock composing Earth
melted, and heavier elements such as iron and nickel sank to the center of the planet, where they remain molten even to today. It must have taken
hundreds of millions of years for Earth to cool enough to allow water to exist as a liquid, but almost immediately after water was available as a
liquid the first signs of life began to emerge.
The beginning of life:
The first organisms were Anaerobic Prokaryotes (more specifically primitive anaerobic bacteria), which means cells whose genetic material was not
contained within a nucleus. These cells obtained nutrients through absorption from their environment. As these cells multiplied, they eventually used
up the organic molecules produced by prebiotic chemical reactions, while carbon dioxide and water were still very abundant. What they were lacking was
energetic molecules - molecules in which energy is stored in chemical bonds. Eventually, some cells evolved the ability to use the energy of sunlight
to drive the synthesis of complex molecules.
Oxygenating our planet:
Water-based photosynthesis converts water and carbon dioxide to energetic molecules of sugar, releasing oxygen as a by-product. This newly emerging
process on the planet Earth formed an abundance of oxygen in our atmosphere.
Oxygen reacts with organic molecules destroying them. Many of today's anaerobic bacteria perish when exposed to what is for them a deadly poison,
oxygen. The accumulation of oxygen therefor exterminated many organisms and fostered the evolution of cellular mechanisms which are capable of
detoxifying oxygen. Eventually this leads to the great advancement for microbes to use oxygen in metabolism.
Hordes of bacteria offered a rich food supply to any organism that could eat them. Early predators were specialized prokaryotic cells that were able
to engulf whole bacteria as prey. These predators were otherwise very primitive in that they were capable of neither photosynthesis or aerobic
metabolism. Around 1.7 billion years ago one of these predators gave rise to the first eukaryotic cell. The first cell to carry DNA from within the
How Humans Evolved
- Some Algae Became Multicellular
- Animal Diversity Arose in the Precambrian Era
- Some Plants Became Adapted to Life on Dry Land
- Some Animals Became Adapted to Life on Dry Land
- Amphibians Evolved from Lobefin Fishes
- Reptiles Evolved from Amphibians
- Reptiles Gave Rise to Both Birds and Mammals
Humans are members of a mammal group known as primates, which includes lemurs, monkeys, and apes. The oldest primate fossils ever to be discovered are
55 million years old. Binocular vision provided early primates with accurate depth perception. Early primates had long, grasping fingers that could
wrap around and hold onto tree limbs - an adaptation to tree dwelling. A large brain facilitated hand-eye coordination and complex social
The oldest hominid fossils are from Africa, dating 6 million years ago (Sahelanthropus tchadensis).
This represents a split between apes
and hominids. The earliest hominids could stand and walk upright. They were shorter, but had nicely developed knees that allowed the leg to straighten
Modern Humans Emerged Only 150,000 Years Ago
- Several species of Australopithecus Emerged in Africa
- The Genus Homo Diverged (2.5Mil Years Ago)
- Advances in Tool Technology
The fossil record shows that anatomically modern humans appeared in Africa about 150,000 years ago. The location of these fossils suggests that the
first Homo Sapiens
Around 90,000 years ago Cro-Magnons appeared which had domed heads, smooth brows, and prominent chins (just like us). They were behaviorally more
sophisticated than Neanderthals. Artifacts from 30,000 year old Cro-Magnon archeological sites include elegant bone flutes, graceful carved ivory
sculptures, and evidence of elaborate burial ceremonies. They were also famous for their cave paintings and use of sophisticated art techniques.
Cro-Magnons and Neanderthals lived Side by Side
Cro-Magnons coexisted with Neanderthals in Europt and the Middle East for perhaps as many as 50,000 years before Neanderthals disappeared from fossil
record. Some researches believe that Cro-Magnons interbred extensively with Neanderthals, thus absorbing them into the human genetic mainstream. Other
researchers suggest the Cro-Magnons were simply over-ran by this superior species. While nobody is for certain, the extinction of Homo
leads us to believe their superior ability of Homo sapiens
to exploit the available resources slowly drove Neanderthals to
[edit on 12/19/08 by Yoda411]