2.2 The history of earth
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Learning objectives
You can describe the origins of the three main types of rock
You can determine the relative age of rock layers
You understand what rock layers and fossils can tell us about the geological history of earth
The origin of Earth
Types of rock
There are three types of rock:
Sedimentary
Igneous (like granite or basalt)
Metamorphic (for example marble)
Sedimentary rock
Formed by layers of sand or clay being deposited on top of each other
Different layers clearly visible (sometimes)
Example: sandstone, claystone, limestone (kalksteen)
Metamorphic rock
Change in rock composition due to high pressure and temperature, for example quartzite (kwartsiet) from sandstone; and marble (marmer) from limestone
Igneous rock
formed by volcanic activity, for example granite or basalt
Fossiles
Fossil: petrified (versteende) remains of plants or animals
In wich type of rock can you encounter fossiles you think: igneous, metamorphic and/or sedimentary rock?
Absolute and relative dating
Relative dating: deepest soil layers are the oldest
Absolute or radiometric dating
You can determine the age of rocks quite precisely
Many rocks contain small amounts of radioactive elements
These radioactive elements disintegrate at a fixed rate. Thus, you can count back how old the rock is
Example: the half-life of uranium-235 is 700 million years. That means that after 700 million years 50% of the radioactive uranium-235 atoms is left (the rest is converted into lead-207).
Mammoth
What does the finding of a fossile of a mammoth at the bottom of the North Sea tell us?
Mammoth
What does the finding of a mammoth at the bottom of the North Sea tell us?
the climate was colder then
the North Sea was once dry
Limestone
What can you tell about the past when you encounter limestone?
Limestone
What can you tell about the past when you encounter limestone?
there was once a sea there
sea creatures once swam in the sea whose lime (kalksteen) skeletons fell to the bottom