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Fossil Evidence of Change
Transcript of Fossil Evidence of Change
Fossil Evidence of Change
Earth's Early History
Land environments – surface of the Earth was rich in “light” elements; densest elements at the core (iron)
Heat was released from cooling interior
Additional heating from meteorites crashing to the Earth
Life would have been consumed by the intense heat
Geologic Time Scale
Divided into Precambrian time & Phanerozoic eon
Next division = era
Each era divided into 1 or more periods
Periods are divided into epochs
Eons Eras Periods Epochs
Clues in the Rocks
The Fossil Record – a book with missing pages
Fossil – preserved evidence of an organism
Only organisms that are buried rapidly in sediment, usually aquatic (water)
Law of superposition – youngest rock layers are on top of older layers
Relative dating – determine age of rocks by comparing them with rocks in other layers (in the same location)
Radiometric dating – uses decay of radioactive isotopes to measure age of rock; can only be done in igneous & metamorphic rock
Half-life – amount of time it takes for half of the original isotope to decay
- Ex: Uranium 238 decays to Lead 206 with a half life of 4510 million years. Measure the amount of uranium to lead to determine the age of the sample.
Carbon-14 dating – used for mummified remains (organic substances), such as bones & tissues; carbon has a short half-life & must be used on samples less than 60,000 years old
Mesozoic era – emergence of reptiles, particularly dinosaurs
K-T boundary – a layer of rock between Cretaceous & Paleogene periods containing iridium (common in meteorites, not on Earth); evidence of dinosaur extinction by meteorite
Atmosphere – maintained by Earth’s gravitational field
Gases were likely those expelled by volcanoes
Water vapor (H2O)
Carbon dioxide (CO2)
Sulfur dioxide (SO2)
Carbon monoxide (CO)
Hydrogen sulfide (H2S)
Hydrogen cyanide (HCN)
LITTLE TO NO FREE OXYGEN
Fossil Formation – does not occur in igneous or metamorphic rock (due to extreme heat and/or pressure during their formation)
Organism dies & buried in sediment
Sediment builds up in layers encasing remains
Minerals replace or fill in the spaces of the bones & sometimes hard parts of organism
Sediment eventually hardens into rock
Paleontologist – studies fossils & from fossil evidence infers diet and environment of organism; can often create images of extinct communities.
Oldest layer with fossils in it
Oldest layer overall
Precambrian – 90% of Earth’s entire history; during this time, autotrophic prokaryotes appeared (like cyanobacteria) and enriched the atmosphere with OXYGEN!
- Glaciation (formation of glaciers) marked second half of this eon
- Cambrian explosion – ancestors of many organisms evolved rapidly for large diversity of life
- At the end of the era, there was a mass extinction – many species become extinct in a short time; occurs every 26-30 million years
Pangea was a large supercontinent before tectonic plates shifted the land masses.
Humans are the dominant land animals