Download GEOLOGICAL TIME The Earth is immensely old

GEOLOGICAL TIME
Humans evolve
11:59:42
Rocks of the Burren form
11:09 pm
The Earth is immensely old - we know
from modern dating techniques that it
is 4,650 million years old. To put this
into perspective, humans evolved only
2 million years ago. By comparison,
the rocks of North Clare range
between approx. 341 million years
and 318 million years old. This is still
relatively young in terms of the total
age of the Earth! This diagram on the
right depicts the age of the Earth as a
12 hour clock. Note how the rocks of the
Burren form only at 11.09 pm, and humans
appear at only 18 seconds to midnight.
This mineral, zircon, contains
uranium and is commonly
used for dating rocks.
12
11
10
Animals
1
2
No life
on Earth
9
3
8
Bacteria and
algae
7
Bacteria
4
6
5
Geological time as a 12 hour clock
How do geologists date rocks? By measuring extremely small amounts of radioactive elements (e.g.
uranium) trapped within minerals in some types of
rock. Radioactive elements transform into other elements over time at a constant known rate, so by measuring the amount of what’s left (often only in thousandths or millionths of a gram) we can work out
how long ago a particular rock was formed.
The oldest rocks in Ireland occur on Inishtrahull, north
of Malin Head. They are approx. 1750 - 1780 million
years ago. The oldest rocks in the world are found in
NW Canada, and they are 4280 million years old.
Rocks of Inishtrahull.