How earth is changing

The theory of techtonic plates is now well established. 

Continental drift happens because techonic plates moving.  

Earthquakes and volcanoes are normaly around the edge of techtoinc plates. 

Evidence from rocks

Rocks give evidence of the earth changing.

Erosion and sedimentation takes place over long periods of time making big changes.

Geologists use other evidence from the rocks like:

• looking at cross-cutting features
• fossils 
• deepness of the rock

This evidence shows the older rocks. to be more accurate of the age of rocks radioactive dating is used.

Alfred Wegener:

came up with the idea of continential drift. At the beginning of the 20th century.

He thought that the Earths continents were joined together, but moved apart over millions of years.

It gave an explanation to why the existence of similar fossils and rocks on continents far apart. 

Before Wegener:

It was thought that mountains formed because the Earth was cooling.

So contracted and formed wrinkels,or mountains in the Earth's crust.

However this would mean that mountains would be spread out evenly over the Earth.

The heating effect of radioactive materials inside the Earths stops it from cooling.

Wegener said that mounatins were made where the edge of drifting continents collided with another 

Wegener's evidnece:

• Same types of fossils were found in South America and Africa

• The shape of the continets fit like jigsaw

• Matching rocks and mountain chains were found in South America and Africa.

In the center of many oceans there are mid-ocean ridges.

This is where the techtonic plates move apart.

Magma from inside the earth oozes out and solidifies.

This is called convection due to heating by the core of the Earth.

This is all called seafloor spreading

It results inthe seafloors spreading a few centimeters each year.

Evidence of chance in the Earth is from the rocks.

Folds and fossils in sedimentary rocks.

The thing we have been able tolook at directly is the Earths crust.

Evidence from earthquakes show that the Earth has a dense core surrounded by a mantle.

The Earth:

1. The crust, which is relatively thin and rocky
2. The mantle, shown here as dark red, which has the properties of a solid, but can flow very slowly
3. The outer core, shown as orange, which is made from liquid nickel and iron
4. The inner core, shown as yellow, which is made from solid nickel and iron