Question

Reflection Questions

Do not answer until you have completed the time scale located on the pages following Table 1.
How long (in centimeters and years) was the Precambrian period compared to the rest of the scale?
How many years and “centimeters” of time separated the dinosaurs and humans on Earth?
How many years and centimeters of time passed before life appeared on Earth?
For how many years of geologic time have humans existed?
Did dinosaurs exist at the same time as mammals? Explain your answer using the geologic time scale.
Table 1
Complete the total time column for the table below to assist with answering the reflection questions. The first one has been completed for you.
bya=billion years ago
mya=million years ago
1cm=10 million years ago



Time Span
Scale
Total Time
Hadean Eon
(Precambrian Time)
4.6 bya – 3.8 bya
460 cm – 380 cm
.8 billion years
Archaean Eon
(Precambrian Time)
3.8 bya – 2.5 bya
380 cm – 250 cm


Proterozoic Eon
(Precambrian Time)

Cambrian Period

Ordovician Period

Silurian Period

Devonian Period

2500 mya – 543 mya

250 cm – 54.3 cm



543 mya – 490 mya

54.0 cm – 44.0 cm



490 mya – 443 mya

49.0 cm – 44.3 cm



443 mya – 417 mya

44.3 cm – 41.7 cm



417 mya – 354 mya

41.7 cm – 35.4 cm


Carboniferous Period
354 mya – 290 mya
35.4 cm – 29.0 cm


Permian Period
290 mya – 245 mya
29.0 cm – 24.5 cm




Triassic Period
Jurassic Period
Cretaceous Period
245 mya – 206 mya
24.5 cm – 20.6 cm


206 mya – 144 mya
20.6 cm – 14.4 cm
144 mya – 65 mya
14.4 cm – 6.5 cm
Tertiary Period
Quarternary Period
65 mya – 1.8 mya
6.5 cm – .18 cm


1.8 mya – Today
.18 cm – 0.00 cm
The Present
Today
0 cm

Answer 1

How long (in centimeters and years) was the Precambrian period compared to the rest of the scale?

542 million years, or 54.2 cm on the geologic time scale.

How many years and “centimeters” of time separated the dinosaurs and humans on Earth?

On the geologic time scale, this corresponds to a span of about 6.5 cm.

How many years and centimeters of time passed before life appeared on Earth?

It is generally believed to have occurred around 3.5 to 4 billion years ago. On the geologic time scale, this corresponds to a span of about 350 cm to 400 cm.

For how many years of geologic time have humans existed?

The first anatomically modern humans emerged around 300,000 years ago, which corresponds to a span of about 30 cm on the geologic time scale.

Did dinosaurs exist at the same time as mammals? Explain your answer using the geologic time scale.

Dinosaurs and mammals did not exist at the same time on the geologic time scale. Dinosaurs lived during the Mesozoic Era, which spanned from about 252 to 66 million years ago. Mammals, on the other hand, evolved during the Late Triassic period, which was about 230 million years ago, but remained small and insignificant until after the extinction of non-avian dinosaurs around 65 million years ago. Therefore, there was a span of about 165 million years between the emergence of the first mammals and the extinction of non-avian dinosaurs.

Here are the total time spans for each time period on the geologic time scale, based on the information you provided:

- Proterozoic Eon: 1.957 billion years (195.7 cm)

- Cambrian Period: 56 million years (5.6 cm)

- Ordovician Period: 44 million years (4.4 cm)

- Silurian Period: 28 million years (2.8 cm)

- Devonian Period: 60 million years (6 cm)

- Carboniferous Period: 64 million years (6.4 cm)

- Permian Period: 45 million years (4.5 cm)

- Triassic Period: 39 million years (3.9 cm)

- Jurassic Period: 62 million years (6.2 cm)

- Cretaceous Period: 79 million years (7.9 cm)

- Tertiary Period: 65 million years (6.5 cm)

- Quaternary Period: 2.6 million years (0.26 cm)

I hope this helps!