deep time 1 Flashcards
how old is the earth
6000 years old?
Archbishop Ussher of Ireland (1654)
Earth was created October 22, 4004 BC (at about 6pm)
12000 years old?
Ussher’s estimate plus the Creation
100 million years old?
Lord Kelvin (1870s)
Based on cooling rates of the Earth from a molten state
300 million years old?
Based on length of time to get the sedimentary rocks deposited
how old is it actually? 4.56 billion years old
catastrophism
Landforms are shaped by a series of GIANT DISASTERS!!!
Earthquakes
Comets
Floods
Unpredictable
Un-understandable
how ancient societies looked at the earth: caused by the gods or demons, etc.
Uniformitarianism (geologic principle)
“present is key to the past”
(ripples on beach in sand today, ripples in sandstone from the past)
founding fathers of geology
James Hutton (present is key to past quote), Charles Lyell
write the first two textbooks on geology
Geologic time
Human understanding of geologic time has changed our perception of time and the Universe.
Two different ways to look at ages
-Relative Dating
-Absolute Dating
relative dating: Original Horizontality in sedimentary rocks
Sediments settle out of water by gravity
Accumulate horizontally
Tilted sedimentary rocks are likely deformed
relative dating: superposition (in sedimentary rock/lava sequences)
Younger beds on top
Oldest beds on bottom
Must be undeformed
relative dating: lateral continuity
Strata often form in laterally extensive horizontal sheets
Erosion can dissect the sheets
become discontinuous because of erosion, bu they used to be one continuous thing
relative dating: cross- cutting relations
Intrusions and faults are younger than the rocks they cut (lines that intrude on the patterns are younger than the original patterned sedimentary)
relative dating: baked contacts
Intrusions bake the surrounding country rock (pre-existing rock)
The baked rock is older
Relative dating: Inclusions
Rocks included in another rock are older than the rock they include
Inclusions are always older than the enclosing material
relative dating: Faunal Succession
Groups of fossil animals and plants occur in a definite chronological order
- Specific fossils are only found within a limited, (usually) narrow time range
stratigraphic column
Depiction of the strata in a region
Drawn to scale (averages)
Grand Canyon stratigraphic column
start putting them together for the entire world creating the geologic time scale
Geologic time scale
Epochs
Smallest time blocks
Periods
Made of many epochs
Eras
Made of many periods
Eons
Made of many eras
Largest time blocks
??
Precambrian “Super-Eon”
Ancient Rocks
Very few fossils
Makes up almost 90% of Earth’s history
Split into three eons
Proterozoic
Archean
Hadean
Phanerozic
Visible Life
Split into three eras
Paleozoic
Mesozoic
Cenozoic
