Lesson 2b Global Features of the Earth

Why is this important to this class? We understand the inner workings of the Earth better than any other planet. Interior activity leaves tell tale signs on the surface of the Earth. (Tectonics) Finding these same signs on other planets gives us information about their inner workings. We will use the Earth as a starting point to understand the Solar System.

From antiquity, we have known the inside of the Earth is hot.

The Earth is filled with a volume of very hot, molten material. When it is inside the Earth we refer to this as magma. On the surface it is lava. Tectonics -- distortion of the earth's crust resulting from the forces within the Earth. Distortions occur within the earth's crust causing structural deformation All tectonics occurs because hot magma rises from inside the Earth, to cooler regions nearer the surface.

The basic process is very easy to understand. Material near the surface of the Earth is cool. The hot material inside the Earth rises toward the surface forcing cooler material to sink. It is this motion that causes all tectonics on the Earth (and terrestrial planets). The interior of the Earth is cooling over time, but all cooling has to take place at the surface of the Earth. Otherwise the heat is trapped inside.

Lithosphere – The rigid outer layers of the Earth consisting of the continental crust, the oceanic crust, and the upper mantle. Asthenosphere -- A zone of the earth's mantle that lies beneath the lithosphere and consists of several hundred kilometers of deformable rock.

Below the mantle is a liquid outer core and inside of that is a solid inner core. Let’s put our crust in perspective. Continental crust is ~ 10 km thick The radius of the Earth is 6,378 km. The ratio of crust thickness to Earth radius is 10km/6378km =

If the radius of the Earth was 10 meters the crust would only be 1.5 centimeters.

While we are at it, lets consider the atmosphere. What is a good estimate of the height of the Earth’s atmosphere?

What is a good estimate of the height of our atmosphere? 1.About 2.5 km. 2.About 25 km. 3.About 250 km. 4.About 2500 km.

Above 25 km, the atmosphere is so thin that only rocket planes can fly. So let’s use that. On a 10 meter Earth radius scale the atmosphere is 2.5 centimeters tall.

How far away is the ISS?

The ISS is orbiting the Earth. How far away do you think the ISS is, when you compare it to the distance to the Moon?

. 1.The ISS is about halfway to the Moon 2.The ISS is about one-tenth of the way to the Moon. 3.The ISS is about one-hundredth the way to the Moon 4.About one-thousandths the way to the Moon

Above 25 km, the atmosphere is so thin that only rocket planes can fly. So let’s use that. On a 10 meter Earth radius scale the atmosphere is 2.5 centimeters tall. The ISS orbits at 350 km. On the 10 meter scale, it is 55 centimeters above the surface. The Moon is 384,000 km away. On this scale it would be 600 meters away.

Interior of the Earth Deepest hole ever drilled in the Earth was by the former Soviet Union. They drilled to a depth of 12.2 km after 24 years of drilling. We get some information from lava that makes it to the surface of the Earth But structure wise, all information comes from seismology. Seismology is the study of earthquakes and seismic waves that move through and around the earth

Earth – A water world?

Waves There are two general types of waves. Transverse and Longitudinal. Earth quakes have both types. They are called S-waves and P-waves

Waves There are two general types of waves. Transverse and Longitudinal. Earth quakes have both types. They are called S-waves and P-waves Which type of wave do you think can propagate through a liquid?

. 1.Only the S-Wave since you can’t push and pull a liquid 2.Only the P-wave since a liquid won’t restore the side- to-side motion 3.Neither S-Waves or P-Waves 4.Both S and P-waves

Model of Seismic activity inside the Earth

Observing arrival of S and P-waves shows the size and liquid nature of the outer core. Reflections and refractions between more dense and less dense regions gives further information about structure. Also, waves move at different speeds through different types of material. So the arrival time of the wave also has information about the internal structure of the Earth.

The Continents

From the time of the early European explorers it was noticed that South America and Africa seem to fit together. Alfred Wegner in 1915 suggested that the two continents were once connected. This was, in part, based on the geologic similarities between the two coasts and the shared fossil species found on each continent. Theory found little favor, because there was no known physical mechanism to push whole continents around.

Important advances World-wide seismometers to measure earthquakes. Discovery of mid-Atlantic rift and stripes of magnetic reversal.

Earthquake Epicenters

Pacific Basin region

Volcanoes of the Earth

Mountain Ranges of the Earth

What is the evidence so far? Majority of Earthquakes occur at plate boundaries. Particularly around the Pacific basin. (The Ring of Fire). The majority of volcanoes are located at plate boundaries. Particularly in the Ring of Fire. Mountain ranges are also located at plate boundaries. The continents appear to be on the move. But what is doing the pushing?