Earth’s History

Question 1

How can we examine parts of earth’s history?

Answer 1

By studying fossils which sre life perserved in rock.

Fossils are used as a basis for the geological time scale.

Question 2

Fossils are not just animal remains, they are also….

Answer 2

• shells
• trees
• footprints
• leaves
• burrows from worms

Question 3

Often times when we see a fossil what is it?

Answer 3

Its is not the original material preserved but a copy of that material which sediments fill.

Question 4

1. Preservation

Answer 4

An organism falls into a tar pit or peat bog
An organism can freeze
An insect can be trapped in amber(hardened tree sap)

Question 5

2.petrification/permineralization

Answer 5

Replacement of original mineral, molecule by molecule with silica/calcite/pyrite

Achived through percolation(water carries some minerals in, other minerals out)

Question 6

3.molds

Answer 6

Original skeletons or shells dissolve while in the rock, leaving a void

Question 7

4.casts

Answer 7

Minerals are carried into molds by percolation. They solidify into casts.

Question 8

5.carbonization

Answer 8

An organism is preserved in a thin film of carbon (ie a leaf between teo rock planes)

Question 9

6.coprolites

Answer 9

Fossils of excrement

Question 10

What is relative dating?

Answer 10

Science of determining the relative order of past events, without necessarly determining their absoloute age.

Question 11

What is conglomerate?

Answer 11

A cemented mix of rounded fragments, deposited in water

Question 12

What are rocks called strata?

Answer 12

They are sedimentary rocks that can become uplifted and the horizontal strata is now tilted.

Question 13

What is absoulte time?

Answer 13

Unlike relative dating, absoloute time deals with placing an actual date on an event. Such as couting rings.

Question 14

What is radioactive decay?

Answer 14

The process known as radioactive decay. Decay of rsdioactive isotope can take place in three main ways: alpha decay, beta decay and electrol capture.

Question 15

Alpha decay

Answer 15

Two protons and two neutrons are emitted from the nucleus of an unstable atom. The resulting nucleus has an atomic number that is 2 fewer and a atomic mass that is 4 fewer.

Question 16

Beta decay

Answer 16

A neutron turns into a proton and an electron is emitted. The resulting nucleus has an atomic number that is 1 more and an atomic mass that hasn’t changed.

Question 17

Electron capture

Answer 17

A proton captures an electron and turns into a neutron. The resulting nucleus has an atomic number that is 1 fewer and an atomic mass that hasn’t changed.

Question 18

Half-life

Answer 18

The half-life of an isotope can range from seconds to billions of years.

Ex. C-14 half-life of 5 730 years
Ex. U-238 half-life of 4.5 billion years

Answer 19

→The time it takes for ½ a sample of an isotope to decay.
Initial Nucleii 1 half life 2 half lives 3 half lives
N0 ½ N0 (½)(½ N0)= ¼ N0 ?

Question 20

Half life

Answer 20

N= amount of sample remaining
N0= initial amount of sample
n= # of half lives
t= time elapsed
t1/2= half life of the substance

Question 21

Uranium-Lead Dating (half-life of 4.5 billion years)

Answer 21

This method is useful for dating the Earth’s oldest rocks, although uranium is not all that common in most rocks so if a rock doesn’t contain any uranium this method can’t be used.

Question 22

Rubidium-Strontium Dating (47 billion years)

Answer 22

This half life is more than 10 times the age of the Earth, making it more accurate for the Earth’s oldest rocks. Rubidium is much more common in rocks and mineral compared to uranium.

Question 23

Potassium-Argon Dating (1.3 billion years)

Answer 23

Potassium is a very common element found in most types of rocks and can date rocks as young as 50 000 years old