Fossils and Geologic Time

How much of the substance remains after three half-lives?

• 50%

• 25%

• 12.5%

• 6.25%

Answer explanation

Each half life changes 50% of the substance. After one half-life, 50% of the Potassium (K) in an object has turned into Argon (Ar).

After two half lives, 25% is still K.

After 3, 12.5% is K and 87.5% is Ar.

The amount goes down by 50% from the previous amount, not from the original total.

Tags

NGSS.HS-PS1-8

The artifacts below were found at an archaeological site. Which ones could be dated with radiocarbon dating?

• bronze spear point

• human bone

• paper/parchment fragment

• a piece of cloth from an ancient mummy

• a carved stone

Answer explanation

For radiocarbon dating to work, the object must have some carbon in it - meaning it needs to have been made of some sort of living material.

A copper spear point has no carbon.

Paper and parchment are made of tree bark, reeds, or animal skins.

Cloth made of inorganic materials was only invented in the last 100 years, so anything older would have been made of plant/animal fibers or animal skins.

Stone does not contain carbon unless it is organic sedimentary rock.

Using ONLY the information in the diagram, what is the best method to determine the relative age of these rock layers?

• radiometric dating

• rock type evaluation

• the law of superposition

• principle of uniformitarianism

Answer explanation

The key words in this question are ONLY and RELATIVE -

There are no ages shown in this diagram, and you can't use radiometric dating because you have no rock samples. Plus, the question is asking for the relative age, not the absolute age.

Different places have rocks in different layers, so you can't assume that sandstone is always older than, say, shale or limestone.

The law of superposition, however, states that rocks on the bottom layer of undisturbed are oldest. There's no evidence of disturbance that would change that, so that is the best way to give a RELATIVE age of the rocks in the picture

The principle of uniformitarianism states that physical laws which apply today applied in the past, which isn't related to the question at all.

Tags

NGSS.MS-ESS1-4

Put the organisms in order of when they first appeared on earth, with 1 being the oldest and 5 the most recent

• reptiles and dinosaurs

• stromatolites

• trilobites

• bony fish

• mammals

Answer explanation

Tags

NGSS.MS-LS4-1

Which statement correctly describes the relative ages of the rock layers shown in the diagram?

• The left part of layer B is younger than the right part

• The left part of layer F is the same age as layer M

• Layer R is older than layer M

• Layer I is older than Layer B

Answer explanation

The law of original horizontality states that rocks form in horizontal layers, and are altered after - so in a situation like this, there was some sort of geologic activity like an earthquake that moved the layers AFTER they were deposited.

That means both parts of layer F are the same age, and layer B is older than F even though they're next to each other.

Tags

NGSS.MS-ESS1-4

with 1 being the OLDEST and 5 the NEWEST, put the rock layers in order of age

hint: E is a fault, a type of geological disturbance

• B

• A

• D

• C

• E

Answer explanation

In order from YOUNGEST to OLDEST:

E

D

A

B

C

The law of superposition states that the oldest layer in an undisturbed rock formation is the lowest one.

The law of cross-cutting relationships states that any feature that cuts across (so, cross-cutting) is younger than the layers it cuts through.

That means that first C, B, then A were deposited.

Then, D intruded through all three layers.

Finally, a geologic event (like an earthquake) happened, which is what E represents.

Tags

NGSS.MS-ESS1-4

Organize the fossil pictures by type

Groups:

(a) Trace Fossil

,

(b) Cast & Mold Fossil

,

(c) Original Remains

• 
• 
• 
• 
• 
• 

Tags

NGSS.MS-LS4-1

NGSS.MS-LS4-2

An index fossil is used in​ (a)   to compare rock layers ​ (b)   because the organism was​ (c)   and​ (d)   .

• relative dating
• in different places
• common over a large area
• lived in a specific era or period
• absolute dating
• can be easily dated radiometrically
• specific to a small area
• lived across many eras

If fossils in layer D are 100 million years old and in layer B they are 110 million years old, how old might are the fossils in layer C? Choose the best answer.

• 90 million years old

• 120 million years old

• 105 million years old

• 50 million years old

Tags

NGSS.MS-ESS1-4

What does phanerozoic mean?

• invisible life

• fossil evidence

• visible life

• multicellular

Answer explanation

From ancient Greek,

phaneros means "visible"

and zōḗ means "life"