Copy into Notes: Seismographs - measure the times at which different seismic waves arrive and record the differences in their speeds Scientists use the measurements to calculate the density and thickness of each physical layer of the Earth.

Scientific Laws, Theories & Hypotheses Hypothesis A scientific hypothesis is a suggested basic solution for an unexplained occurrence that doesn't fit into a currently accepted scientific theory & is testable, measurable & falsifiable. An idea that hasn't been proven yet. If enough evidence accumulates to support a hypothesis, it moves to the next step — known as a theory — in the scientific method and becomes accepted as a valid, very detailed explanation of a phenomenon.  Experimental data do not prove a hypothesis “right” or “wrong.” Data only either supports or does not support the proposed hypothesis being tested in an experiment.

Scientific Laws, Theories & Hypotheses Laws are statements — often mathematical descriptions — of natural phenomenon or unifying concept; for example, Newton's Law of Gravity or Mendel's Law of Independent Assortment. These laws simply describe the observation. Not how or why they work. Start by understanding & identifying appropriate LAWS in use. Develop a hypothesis. Test/Gather data. If it supports the hypothesis, develop a theory.

Alfred Wegener and Continental Drift In 1915, Alfred Wegener, wrote his hypothesis of continental drift. Continental drift states that the continents once formed a single landmass, broke up, and drifted to their present locations. But I have evidence!

Continental Drift Theory Continental drift explains why fossils of same plant and animal species are found on continents on different sides of Atlantic Ocean.

Pangaea – Greek meaning for “all earth”. Modern Day Earth

Sea-Floor Spreading – process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies. Mid ocean ridge Mid-ocean ridges are geologically active, with new magma constantly emerging onto the ocean floor and into the crust at and near rifts along the ridge axes. The crystallized magma forms new crust of basalt (known as MORB for Mid-Ocean Ridge Basalt) and gabbro. The oceanic crust is made up of rocks much younger than the Earth itself: most oceanic crust in the ocean basins is less than 200 million years old. The crust is in a constant state of "renewal" at the ocean ridges. Moving away from the mid-ocean ridge, ocean depth progressively increases; the greatest depths are in ocean trenches.

Magnetic reversals serve as evidence for sea-floor spreading Metallic minerals in the bands of rocks in the sea floor will arrange themselves in accordance to the magnetic field of the Earth at the time of their creation. As the Earth changes its polarity (North Pole becomes South Pole), the minerals will line up accordingly producing a measurable pattern.

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