Cambrian Explosion-Interactive Videos

Hi guys, I found this excellent video about The Cambrian Explosion on youtube.


PART I   http://www.youtube.com/watch?v=qKMKYd0WSV0
PART II  http://www.youtube.com/watch?v=PPkSMTQc8Cw


The Cambrian Explosion relates to an abrupt appearance of a wide range of organisms, mainly invertebrates, with hard (fossilizable) parts in Cambrian strata, which mainstream scientists date from about 540 million years ago. They were complex, well-developed organisms with many types of differentiated cells, and it is widely conceded that evolution of these organisms from unicellular precursors within such a short period of time is highly doubtful. 

Now, it can be granted that organisms without skeletons will leave few if any fossils, so it should not be too surprising if one evolving line were to appear suddenly in the fossil record. It is surprising, however -- at least within an evolutionary framework -- that such a wide variety of fossilizable forms should appear at more or less the same time. The number of radically different body plans which appear in such a very short period of geological time (about 13 million years according to mainstream science) is greater than at any other. Accounting for the abrupt and sudden appearance of these organisms is one of the leading challenges in evolutionary biology.


http://www.pbs.org/wgbh/evolution/library/03/4/l_034_02.html

Precambrian Era

• The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4570 Ma (million years) ago to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of geologic time.
• Not much is known about the Precambrian, despite its making up roughly seven-eighths of the Earth's history, and what little is known has largely been discovered in the past 50 years. The Precambrian fossil record is poor, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.
• It is thought that the Earth itself coalesced from material in orbit around the Sun roughly 4500 Ma (4.5 Ga) and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that came together to form the Moon (see Giant impact hypothesis). A stable crust was apparently in place by 4400 Ma, since zircon crystals from Western Australia have been dated at 4404 Ma.

Here's a short video about the Precambrian Era

http://www.youtube.com/watch?v=gvtsSejT-NI

Sources:

www.youtube.com
www.wikipedia.com