SME
Grade 12 Science · Earth & Space Science
Earth's history: the early Earth, its atmosphere and the history of life
Use this for “If Earth’s 4.6 billion years were squeezed into one day, at what clock time did an event 2,300 million years ago happen?”
Diagram
2,300
million
years
ago
is
2,300
4,600
=
50%
of
Earth’s
history.
The same share of the day’s 1,440 minutes is 720 minutes, so the event falls at 12:00; the shaded part of the day is everything since.
This is an example. Type your own values to start a new problem.
A
How long ago
example · million years
p
Share of Earth’s history since then
worked out (not typed) · %
m
Minutes before midnight
calculated · minutes
t
Clock time
calculated · hours
Formulas
p
=
A
4,600
×
100
50
=
2,300
4,600
×
100
m
=
p
100
×
1,440
720
=
50
100
×
1,440
t
=
24
−
m
60
12
=
24
−
720
60
Assumptions
•
Earth formed about 4,600 million years ago: midnight at the start of the day.
•
Today is the next midnight, so each hour stands for about 192 million years.
•
Event ages are rounded; new finds move them.
Step-by-step
WE KNOW
A = 2,300 million years
FIND
share of Earth’s history since then (p), minutes before midnight (m), clock time (t)
Step 1 · Find share of Earth’s history since then (p)
Use p = A ÷ 4,600 × 100
The event’s age as a share of Earth’s whole 4,600 million years.
p
=
2,300
4,600
×
100
p
=
0.5
×
100
p
=
50%
Step 2 · Find minutes before midnight (m)
Use m = p ÷ 100 × 1,440
The same share of the day’s 1,440 minutes comes before midnight.
m
=
50
100
×
1,440
m
=
0.5
×
1,440
m
=
720
minutes
Step 3 · Find clock time (t)
Use t = 24 − m ÷ 60
Turn the minutes into hours and count back from midnight, hour 24.
t
=
24
−
720
60
t
=
24
−
12
t
=
12
hours
(12:00
noon)
Check
Put the numbers back in. Both sides should match.
50
=
2,300
4,600
×
100
✓
720
=
50
100
×
1,440
✓
12
=
24
−
720
60
✓
Topic check
See what you know: 5 questions on this topic
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