Earth, Models, and Density

Imagine you are an explorer in the 1400s

What inferences could you make about the shape of the earth based on what you saw?

Would you just fall off?

Why does it appear like the earth really is flat? (Because it is so large)

Time line of earth’s models – we keep changing our minds… 1 st -2 nd century B.C. = Early Greek philosophers believed the earth was flat. 6 th century B.C. = Pythagoras and other philosophers thought the earth may actually be spherical AD Edmund Halley proposed that the earth is hollow.

Some early models of the earth

Our current model of Earth We think the earth has inner layers. Each layer blends with the other layers where they touch. Density and temperature increase toward the center

Let’s start with the layer we know best – the CRUST (write two of these in your flipper) If the whole earth were the size of an apple, the crust would be as thick as the skin of the apple. About 5-10 km thick – thickest under mountains

Let’s start with the layer we know best – the CRUST (write two of these in your flipper) The crust is made of many interlocking pieces, like a puzzle. These pieces are called TECTONIC PLATES.

Let’s start with the layer we know best – the CRUST (write two of these in your flipper) The crust is a solid Temperature of about 15 o C Density (average) of about 2.5 to 3.5 g/cm 3 Made of oxygen, silicon, aluminum, iron, and calcium

Now, let’s move to the layer we know second best – the OCEANS (write 2) Oceans have solid crust underneath. Oceans are on top of crust because they are less dense than crust – 1.2 g/ml Why are oceans more dense than lakes?

Now, let’s move to the layer we know second best – the OCEANS (write 2) Oceans are liquid Temperature of about 10 o C Made of hydrogen, oxygen, sodium (pretty small atoms)

the ATMOSPHERE (write 2) Atmosphere is made of gasses Temperature of about 5 o C Made of nitrogen, oxygen, carbon, helium (pretty small atoms)

the ATMOSPHERE (write 2) Density of about g/ml Why is the atmosphere above the ocean?

Under the crust is the MANTLE (write 2) The mantle is the thickest layer and makes up 80% of Earth’s volume The mantle is about 1000 km thick!

Under the crust is the MANTLE (write 2) The mantle is in between a solid and a liquid = plastic The rock is so hot that it is melted – kinda flows like toothpaste.

Under the crust is the MANTLE (write 2) The mantle has a density of about 5.0 g/ml (average) It is more dense toward the core

Under the mantle is the OUTER CORE (write 2) The crust is solid rock and the mantle is melted rock. The outer core is so hot that the rock has turned to complete liquid.

Under the mantle is the OUTER CORE (write 2 – split top tab in half) The outer core is pretty dense – about 9.8 g/ml The outer core is made mostly of iron and nickel – very dense elements.

At the very center of the earth is the INNER CORE (write 2 – split top tab in half) If the crust is solid, the mantle is plastic, and the outer core is liquid, what do you think the consistency of the inner core is?

At the very center of the earth is the INNER CORE (write 2 – split top tab in half) Wrong – the inner core is under so much pressure from the layers above that its molecules are compressed together to form a solid.

At the very center of the earth is the INNER CORE (write 2 – split top tab in half) The inner core is very dense – almost 13 g/cm 3 The inner core is very hot – more than 7500 o C – hotter than the surface of the sun!

At the very center of the earth is the INNER CORE (write 2 – split top tab in half) The inner core is almost all iron – a very dense mineral. The inner core is about ½ of the radius of the whole earth

How do we know? Has anyone ever been to the core of the earth? What would happen the minute the drill bits hits the mantle? We learn from earthquakes… but that is another story.