Geologic Time Scale & Age of Earth Flashcards
______ time puts numbers and dates on things
absolute
The geologic time scale is a way of ________ the different time periods - and the whole time the earth has been in existence.
organizing
The geologic time scale is a visual ________ of geologic time
representation
What is the geologic time scale?
a visual representation of geologic time
The geologic time scale is based on…
the succession of rock layers
The geologic time scale is divided into:
Eons-> Eras -> Periods -> Epochs
What is the Precambrian supereon?
the period of time on the Earth before there was any life on Earth
About 600 million years ago we began which eon?
Phanerozoic
The Phanerozoic eon includes which three eras?
Paleozoic, Mesozoic, Cenozoic
The Paleozoic era was marked by…
single cell life that developed into mostly ocean-dwelling creatures
The Paleozoic era was marked by ______ cell life that developed into mostly ocean- ______ creatures.
single, ocean
The Mesozoic Era was the Age of the…
Dinosaurs
The Cenozoic Era has been named the Age of the…
Mammals
which eon are we currently in?
the Phanerozoic eon
which era are we currently in?
the Cenozoic era
What are Eras further divided up into?
Periods
how long to periods last?
millions of years
The starting and ending dates of most periods are based on…
fossil groups
Some period boundaries are marked by ______
extinctions.
Periods are further subdivided into…
epochs
Some of the earliest attempts at estimating the Age of the Earth are based on…
sedimentation, and thickness of the strata
The earliest attempts at estimating the Age of the Earth looked at a series of rock _____ and figuring out how long it might have taken to ______ all of those rock units.
units, deposit
To conduct accurate estimations of the age of the earth based on sedimentation you would need to assume that there was…
a constant record of deposition and no weathering/erosion
Sir Halley came up with a method to estimate the age of the earth by looking at…
the oceans, and how much salt is dissolved in the oceans.
Sir Halleys theory is that if you could assume that the oceans were originally ________, how long would it have taken for them to accumulate the amount of _____ that they have today
freshwater, salt
By using Sir Halley’s method what was the estimated age of the earth?
90 million years.
What were the flaws of Sir Halley’s method?
- you need to assume that the ocean started at 0% salinity (which isn’t necessarily true)
- you need to assume that the salt content doesn’t vary (which isn’t necessarily true: salt content can be lost through tectonic, biologic processes)
How can salt content be lost in the ocean?
through biologic, tectonic processes
What was Darwin’s estimate of the age of the earth based on?
the time it would be necessary toe rod a particular mountain range in Europe
How old did Darwin estimate the Earth to be?
300 million years old
who challenged and rejected Darwin’s theory/method?
Lord Kelvin
what was Lord Kelvin’s estimate of the Earth based on?
thermodynamic cooling
Lord Kelvin assumed that the Earth was once completely ______ _____, which is a temperature ranges between ____-____ degrees Celsius
molten rock, 800-1200
Lord Kelvin assumed that the Earth has been cooling since its original molten rock state, what did he calculate to get an age of the Earth?
he calculated how long it would take for the Earth to cool down to its current temperature
How old did Lord kelvin estimate the Earth to be?
20-100 million years
what were the flaws with Lord Kelvin’s thinking?
- He needed to assume that no heat was added to earth after its formation, which was proven to be not true by the discovery of radioactivity by Marie Curie
what discovery invalidated Lord Kelvin’s theory?
the discovery of radioactivity
What is radioactivity?
the breakdown of unstable elements that releases energy in the form of heat
who discovered radioactivity?
Marie Curie
Radioactivity is the _______ of unstable elements that releases energy in the form of ______
breakdown, heat
What do modern estimated base their estimation of earth’s age on?
theometric dating
What do modern estimated base their estimation of earth’s age on?
radiometric dating
How old do modern scientists estimate the Earth to be?
4.55 billion years
Radioactive elements are unstable ______ of an otherwise stable element.
isotopes
radioactive elements are important to…
figuring out the age of geologic materials as well as in environmental questions
how any radioactive elements have been discovered?
> 1500
Radioactive elements are ______
unstable
Radioactive elements are unstable which means they _____ into stable _____
decay, stable
Decay occurs at _____ rates for each type of radioactive element
different.
The rate at which an element decays is known as…
an element’s half life
a gigabite is ______ bites, a gigayear is _____ years
1 billion, 1 billion
What is a half life?
a measure of how quickly a radioactive element decays
A half life is a measure of how quickly a ______ element decays.
radioactive
A half life is the time needed for half the _____ atoms in a sample to decay
parent
What are the parent atoms?
the unstable radioactive atoms
What are the daughter atoms?
the stable elements that the parent elements decay into
Parent atoms are the ______ radioactive atoms
unstable
Daughter atoms are the _____ elements that the parent elements decays into
stable
If you know the half life of an element and the initial concentrations of parent and daughter atoms you can calculate…
age.
The oldest sedimentary rock mineral has been dated to _____ billion years
4.4
however we know that sedimentary rocks are formed from other rocks, so we would assume that there was an older rock that formed the sedimentary rock
We determine the age of the Earth by coming at it from a ______ way, with the assumption, and strong evidence, that the whole solar system formed in the same event
roundabout
By assuming that the whole solar system formed in the same event, what can we assume?
that the earth is the same age as the rest of the planets and the rest of the material in the solar system
What is the Allende meteorite?
a carbonaceous chondrite,
a carbonaceous chondrite contains tiny amounts of ______
carbon
