What are the major pieces of evidence that support the theory of plate tectonics?
1) Shape of the continents: Most of the major continental masses look as if they fit together like a jigsaw puzzle along their coastlines. In particular, people notice that South American fits almost exactly into Africa. We now know through other pieces of of evidence that all continents were indeed once all joined together as one land mass - a supercontinent called Pangea. 2) Location of mountain ranges and fossils: If you "reassemble" all the continents, the ancient mountain ranges and the location of rock types and index fossils all match up. 3) Earthquakes and Volcanoes: Mapping the locations of earthquakes over time has shown that almost all of them occur along plate boundaries. Similarly, most active volcanoes on Earth are found along plate boundaries as well. These locations, when mapped, define a clear boundary. 4) Hot Spot Volcanoes: Hotspots are localized intense zones that can melt the overlying crust and form a volcano, and they are independent of what is happening in the crust. This results in volcanoes that are not related to the position of the plates and their accompanying boundaries, and therefore most do not occur near a boundary. When the plates move away from the hotspot, the hot spot volcano no longer has the necessary heat and becomes extinct. The new area of plate above the hot spot then melts and a new volcano is formed. This process results in a chain of volcanoes, with the active volcano over the hotspot and the remains of volcanoes which get older and older as you move away from the hotspot. Ex: Hawaiian Islands. 5) Seafloor Spreading: At mid-ocean ridge spreading centers, magma rises up through the mantle and new oceanic crust is created. The age of the oceanic crust increases with distance away from the ridge crests. We can use age-dating techniques to figure out the ages of the rock to confirm this. In addition, magnetic minerals in the magma align with Earth's current geomagnetic field at the time of cooling. When Earth's geomagnetic field undergoes a reversal, the change in polarity is recorded within the magnetic minerals in the rock layers. This contributes to the alternating pattern of magnetic striping on the seafloor.
How do scientists know what the Earth's interior is made of?
Scientists use seismic data to see where within the Earth that seismic wave speed changes. P-waves arrive at the detector first which means they move faster, and they can travel through both solids and fluids. S-waves arrive at the seismic detector second which means they move slower, and they can only travel through solids. Plotting the seismic wave paths and their velocities is how scientists have determined the internal composition of the Earth. The velocity (speed) of the wave increases with temperature, so scientists can identify areas in the mantle that are hotter and cooler. In combining both of these aspects - paths of P- and S-waves, and velocity of the waves - scientists can build 3D models of the Earth's internal structure. Another important aspect to take into account is refraction, or a change in wave direction due to a change in rock/fluid type. A second important aspect to take into consideration is reflection, or a when a wave impinges on a change in rock type. Using seismic data from the velocities of p- and s-waves, scientists have determined the internal structure of the earth. The inner core is solid (mainly composed of iron and nickel), the outer core is liquid (again mainly composed of iron and nickel), the mantle is made up of molten rock, and the crust is made up of different rock types.
What is the relationship between the Earth's atmosphere and weather and climate?
The Earth's atmosphere is the sole reason we have both weather and climate. Our atmosphere is an amalgamation of many essential gases and water vapor that exists for about 82,000 miles above the surface of the planet. The atmosphere helps to trap heat from the Sun from escaping back into space, which keeps the surface temperatures at a habitable levels allowing for life to exist here. The atmosphere is also essential in keeping water vapor trapped within the Earth system to allow for the cycling of water through processes such as evaporation, condensation, precipitation, transpiration, and sublimation. The water vapor found in Earth's atmosphere in the form of clouds and precipitation determines the weather and climate, which are related but different in terms of time scales. Weather is the state of the atmosphere for a particular location at a specific point in time. Climate is the average weather patterns for a particular location taken over a long period of time. Temperature and precipitation - two key factors in describing weather and climate - are determined by atmospheric conditions. The amount of heat and moisture (water vapor) that the atmosphere retains in a particular location will determine the weather pattern for that area, and therefore averaged over long periods of time, climate as well.