A very comprehensive summary (including images, tables and keywords; 8 pages, 2375 words) of chapter 2 of the Eduhint TTO method for the third grade.
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- First, the earth was glowing hot and molten.
o The earth slowly cooled down, and the crust and mantle were formed
- As a result of the volcanic activity, water vapor and CO 2 entered the atmosphere. The water
vapor condensed and seas were formed.
- About 3 billion years ago, bacteria formed that absorbed CO 2 and emitted oxygen.
o This oxygen created possibilities for new life forms
The geological history
- At first, life only consisted of bacteria, but than new lives emerged: molluscs, shellfish, fish, land
plants, reptiles and mammals. This evolution has 4 main stages:
1. Precambrian – continents appeared and the Earth froze, possibly several times. The
land surface was bare. There was only life under water. At the end of this era, life on
land began.
2. Paleozoic – before this era the continents had moved apart, but in this era, they moved
back again to form Pangaea
3. Mesozoic – the time of the dinosaurs. Pangaea moved apart and the current continents
started to form
4. Cenozoic – the youngest era started when the dinosaurs died. Life came into being as its
known for now.
A coming and going of species
- Five times, all life on earth disappeared, the causes of this mass extinctions are diverse.
o Some millions years ago it became colder, covering the earth in large parts of ice. The
amount of CO2 decreased, which disrupted the food chain
o 65 million years ago, it is believed that a large meteorite caused a lot of dust in the
atmosphere. Blocking the sunrays, and therefore there was not enough light for plant
growth.
Learning objectives
- You know how the earth has changed over the past 4.5 billion years
- You understand the reason why life on earth underwent such big changes
- You can use the geological calendar to distinguish differences between eras
, 2.2 The history of Earth
Rocks and fossils
- The history of the earth is found out by the studying of found rocks and the fossils in these.
o A fossil is a fossilized remain of (part of) a skeleton, or an
imprint of an animal or plant.
o A fossil must be buried quickly under mud or sand before it can
decay or disintegrate.
- Rocks and fossils provide a lot of information about the conditions and
climate of the past.
- If there is a fossil found of a mammoth at the bottom of the North sea,
you can conclude that there used to be land there, and that it was
much colder in that area in the past.
- When there is found a layer of limestone, you can conclude that long
ago, calcareous remains from dead marine animals fell to the bottom
of the sea and therefore that there used to be a sea at the site of the
limestone.
o If there are ammonites in that stone, you know that the sea
must have been there between 250 and 65 million years ago.
- Ammonites are index (or trace) fossils
o The shorter a species lived, the more precise a rock layer can
be dated
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