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Pre-Cambrian Era

Welcome to the Planet of Molten Rock...
by

Blainers & Jake Ging-Pot

on 15 March 2010

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Transcript of Pre-Cambrian Era

Pre-Cambrian Eon Hadean Defining Characteristics:
Formation of Earth's crust & main bombardment
Continuing Erosion and Plate Tectonics have destroyed Hadean rocks 4.6 to 4.0 Million Years Ago Name comes from the Greek underworld, Hades. Earth's surface was molten Formation of Earth:
Condensation around the sun that attracted cosmic material; enormous amounts of heat melted the materials together, allowing them to seperate and form layers (iron core, silicate, mantle, thin outer crust) Planets of matter that created the Earth were dust particles and small planets called planetismals. This was a violent time in the solar system (proved by craters on other planets) Earth's violent atmosphere is believed to have been comprised mostly of nitrogen or CO2. Some sedimentary rocks formed later in the Hadean which implies the existence of surface water. Acasta Gneiss is a 4 billion year old rock in Canada, composed of quartz and feldspar (possibly derived from granite) Proterozoic Defining Characteristics:
First multicellular animals at the end of the interval
Major mountian building episodes
Oldest known glaciation Greek for "First Life" 2,500 to 543 Million Years Ago Oxygen was "created" and it is believed to have been toxic to some early life forms Small bodies of water like tide pools developped from all the erosion of tectonnic plates and mountain building, diversifying life Life was mainly single-celled bacteria and cyanobacteria Cyanobacteria
Formerly called blue-green algea
Probably played a major part in oxygenating the Earth's atmosphere
Oldest recorded fossils Appearence of eukaryotes
Organisms with cells that have membrane-bound nuclei and organelles (mitochondia, plastids, etc.) Most common eukaryote fossils in this era
were the acritarchs (single-cells with
acid resistant walls) Oldest known multicellular
eukaryote is Grypania Spiralis
2.1 Billion Years Old
Found in Michigan Earliest known multicellular animals (Ediacaran fauna) resembled jellyfish and segmented worms, but some were so bizzare that they cannot be classified. Glaciation- large amounts of snow and ice covering the ocean; believed to have gone as far south as Equador; "Snowball Earth" phase
Grypania Spiralis Acasta Gneiss Archaen 3,800 to 2,500 Million Years Ago Formerly known as "Archaeozoic" Heat flow was 3x higher than it is today Most surviving Archaen rocks are metamorphic or igneous Volcanic activity was higher with numerous hot spots, rift valleys, and lava eruptions No large continents until late-Archaen High rate of geologists activity Barrage of particularly large impactors known as the "Late Heavy Bombardament" (climax of violent era) Atmosphere was thought to have lacked free oxygen Liquid water present Sun was about 1/3 dimmer than present day
May have contributed to lower global temperatures Large amounts of green-house gasses By the end of the Archaen era, plate tectonics may have been similar to today The oldest recorded fossils of life on Earth are of the cyanobacterial mats (stromatolites) Life may have been limited to simple non-nucleated, single-celled organisms called "prokaryota" No known Eukaryotic fossils No fossil evidence of intra-cellular replications, like viruses Jake RYchlak & Kym Blain
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