Astronomy

A. Dayle Hancock

adhancock@wm.eduSmall 239

Office hours: MTWR 10-11am

http:// physics.wm.edu/~hancock/171/

The Earth ● What Powers the Earth's atmosphere, oceans and land

● The Earth's Interior● Continental movement.● The Earth's protection from changed subatomic particles

● How Life has transformed the atmosphere

● Patterns of weather● How humans are changing our habitat

The Earth is very Active

2

Earth's Oceans

3

The Earth's oceans have a major impact on the earth. All of the water on Earth (Oceans, fresh water, polar ice caps etc) would make a sphere 860 miles in diameter. Currents constantly move through the oceans. Without water, life would not exist on Earth. Only Earth of the terrestrial planets has large amounts of liquid water.

Earth's Atmosphere

4

The Earth's atmosphere is constantly in motion. The atmosphere extends out to 300 km but 80% of the atmosphere is within 16 km of the surface. The earth's rotation, heat from the Sun and interaction with the oceans produce clouds, storms and cyclonic storms (hurricanes). Convection currents in the air and water constantly re-distribute the energy in the atmosphere and oceans.

Eartrh's Surface

5

The Earth's surface is also active but normally on much longer time scales than the atmosphere and oceans. The rocks at the bottom of the grand canyon are 1.7-2.0 billion years old but the rocks at the top are only ¼ billion years old.

Energy that Drives the Activity

6

Energy that drives all this activity comes from two main sources: the Sun and the internal heat of the Earth. The

Internal heat energy is due to heat from the formation of the planet and radioactive decays of heavy elements.

Green House Effect

7

39% of the light reaching the Earth is reflected back into space. The remainder heats the Earth's surface. The Stephan-Boltzmann and Wien's law tells us that the heated surface emits infrared

radiation according to its temperature which is radiated back into space. Using only this model, the surface of the earth would be 254 K (-19oC or -2oF). The Earth would be frozen and life could not exist.

8

Green House Effect

The actual average surface temperature is 287oK (14oC or 57oF). What causes this higher (more life friendly temperature)? Some molecules in the atmosphere trap the infrared radiation from escaping.

The molecules that are most effective are water (H20), carbon

dioxide (C02) and methane (CH

4). This is called the green

house effect. It is the same effect that causes the inside of your car to be warm on a sunny day when the air is cold.

The Earth's Interior

9

After the early Earth formed, the heavier material (mostly Iron, Fe) descended to the center of the Earth. Lighter material like silicates 'floated' upward.

The Earth's Interior

10

Over time, the iron formed a solid inner core. A liquid iron core surrounded the solid iron core. The mantel was formed with a mixture of iron and other silicate materials. The mantel is a solid but 'plastic' in that it can deform without breaking or cracking. Lighter material like silicates 'floated' upward to form the crust.

11

The Earth's Interior

How do we know the structure of the interior of the Earth? Earthquakes and other 'events' send seismic waves through the Earth. There are two types of seismic wave: S waves are transverse waves. P waves are longitudinal waves. Each bend differently when they pass through different densities and compositions in the Earth's interior.

12

The Earth's Interior

The lower figure show the temperature and melting point of the material in the Earth interior.Although the temperature is almost the same in the lower liquid core and solid core, the solid core is below the melting point. Also note the the thin layer that is molten below the crust.

13

Plate Tectonics

In 1915, Wegener suggested that the continents fitted together 200 million years ago to form one giant continent called 'Pangaea' Over time, Pangaea broke up to form the current continents. This idea was not excepted by most geologist at the time.

14

Plate Tectonics

In the 1950s it was discovered that material was being forced upward from the mantel that formed the mid-Atlantic underwater mount range. This was moving Europe and North America apart at a rate of a few cm per year much as Wegener had suggested.

15

Plate Tectonics

By the 1960s geologist identified the major tectonic plates of the crust. At the boundaries of the plates, earthquakes occur, mountain ranges are pushed up and there are often volcanoes.

16

Plate Tectonics

Where tectonic plates collide, deep ocean trenches are formed along with mountain ranges on the continental plates. At rift zones in the ocean, underwater mountain ranges are formed. Motion of the plates is caused by convection currents in the asthenosphere.

17

More Plate TectonicsThe Himalayas formed when the Indian plate collided with the Eurasian plate

The African plate is pulling away from the Arabian plate which formed a riff. The riff flooded to form the Red Sea.

Types of Rocks

18

Igneous rock is formed when magma (molten rock from beneath the surface) escapes as lava and cools to a solidSedimentary rock when loose particles of sand and rock are fused together with other minerals.Metamorphic rock is formed when igneous or sedimentary rock is subjected to high temperature and pressures deep in the Earth's crust.

Magnetosphere

19

The Earth's rotation and molten core produce a magnetic field through the dynamo effect. The Earth is constantly bombarded by the solar wind. The solar wind is mainly protons and electrons from the Sun's hot corona that travel at ~400 km/s (1 million miles/hr).

Magnetosphere

20

The Earth's magnetic field is pushed back by the solar wind to form the magnetosphere. The charged particles of the solar wind become trapped in two torus (donut) shaped regions around the Earth know as the Van Allen belts. The magnetic field of the Earth protects life on the surface from the effects of the solar wind.

Aurora

21

When the Van Allen belt is overloaded with trapped charge particles, they leak out at the weakest point in the magnetic confinement near the north and south magnetic poles. When this happens, the charged particles excite oxygen atoms in the upper atmosphere producing the green colored Aurora. The ring shape seen from space (upper image) show the weak place where the charged particles 'leak' out of the Van Allen belt.

Magnetic Field Reversal

22

Geological evidence as well as computer simulations indicate that the Earth's magnetic field 'flips' (north to south or vice verse) every 300,000 year (most recently 780,000 year ago). When lava cools after being pushed up from the Mid-Atlantic range, the magnetic field is 'frozen' into the rock. As the riff widens, the sea floor contains a record of information about the direction of the Earth's magnet field over geological times.

The Atmosphere

23

The Earth's early atmosphere was mainly water. Intense volcanic activity released large around of C0

2 and ammonia

(NH3). Much of the C0

2

dissolved in the oceans and combine with calcium or other elements to form carbonates (like marble and limestone). The ammonia was broken down by UV radiation to nitrogen and hydrogen. The hydrogen escaped into space

Life Changes the Atmosphere

24

Single cell organisms appeared over 3 billion years ago. These early organisms converted light into energy through photosynthesis. This process converts C0

2 and

water to energy and O2.

Over time photosynthesis produced the levels of O

2

we see in our current atmosphere. Animals evolved which used the O

2

for respiration.

Comparing Terrestrial Planet Atmospheres

25

The terrestrial planets with atmospheres (Mercury has no atmosphere) are very different. Venus being closer to the Sun and warmer boiled off any liquid water and made it impossible for carbonates to form. This trapped the CO

2 and

resulted in a large green house effect and a very high surface temperature. The temperature on Venus is 460oC (855oF)

Comparing Terrestrial Planet Atmospheres

26

The situation on Mars was very different being further away from the Sun and colder. The CO2 was driven into rocks and the water froze. The surface temperature is cold. The atmosphere has became very thin. The atmospheric composition is similar to Venus but the Martin atmosphere is 10-4 as dense as Venus.

Comparing Terrestrial Planet Atmospheres

27

On Earth the atmosphere was well suited for life which changed the atmosphere over time. In general:

The closer a terrestrial planet is to the sun the stronger the greenhouse effect and the higher the planets surface temperature

Life on earth depended on our distance from the Sun.

Pressure in the Earth's Atmosphere

28

The pressure in the Earth's atmosphere decreases at higher altitudes. The change is smooth but 'nonlinear'. The temperature changes (first colder then warmer then colder and finally warmer again) as the altitude increases.

The Atmosphere

29

Because the poles are cold and the equator is warm, convection would cause hot air to rise from the tropics and flow towards the poles where it would cool and sink, returning to the topics.However, the rotation of the Earth breaks up this overall convection into a series of convection cells. The movement of the air can be in different directions at different altitudes.

The Upper Atmosphere

30

In the stratosphere (12-50 km above the surface) some of the oxygen is in the form of ozone (O

3). Ozone protects the

surface of the planet from UV radiation. In the 1970 it was discovered that the ozone was being depleted primary because of chlorofluorocarbons (CFC) and other halogenated chemical used as refrigerants, solvents and other applications. Reduction of CFC production and use as greatly reduced the ozone 'hole'.

The Atmosphere

31

Clearly life on earth has effected the thin layer of the earth that we call the biosphere. The biosphere depends on the temperature of the oceans and atmosphere. About equal parts of the O

2 comes from

plant life and phytoplankton in the ocean.

Human Effects on the Biosphere

32

The world population has grown exponentially since the industrial revolution. With the growth in population, demands on the Earth's resources have also increased exponentially. Deforestation of the Amazon basin because of

farming, grazing and illegal logging is one example. The depletion of the ozone layer is another.

Climate Change

33

Since the industrial revolution, fossil fuels (oil, coal, natural gas) have been increasing used. These fuels produce CO

2 which has increasing built up in the

atmosphere. As we have seen CO2 is a greenhouse gas.

34

Climate Change

As this plot shows, the surface temperature of the Earth as increased with the CO

2

concentration in the atmosphere. If nothing is done to slow the use of fossil fuel, global

temperatures will increase by 2-4o C in this century. This could result in the melting of the Antarctic ice shelf and Greenland sheet causing sea level rises. Colder oceans could result in low phytoplankton levels resulting in less CO

2 being removed from the atmosphere.

Climate Change Is Real Senator Inhofe