Seafloor Spreading HypothesisIn the 1960s, scientist Harry Hess proposed the Seafloor Spreading Hypothesis, which provided key evidence for plate tectonics. According to this idea, new oceanic crust forms at mid-ocean ridges as magma rises from below Earth's surface. As the new crust cools and solidifies, it pushes the older crust away from the ridge, causing the seafloor to spread. This process helps explain how continents move and why ocean floors are younger near ridges and older near...

Magnetic Evidence for Seafloor SpreadingOne of the strongest pieces of evidence for seafloor spreading comes from magnetic patterns recorded in oceanic rocks. Earth’s magnetic field has flipped many times, meaning the north and south magnetic poles have switched places. When molten rock cools and solidifies at mid-ocean ridges, the magnetic minerals inside align with Earth's magnetic field at that time. These alternating magnetic stripes on the ocean floor prove that new crust constantly...

Earth's Mantle Beneath the Earth's surface is a thick layer of rock called the mantle. It sits between the crust and the core and makes up most of the planet's volume. Even though the mantle is solid, it moves very slowly over time. This movement helps shape Earth's surface by driving plate tectonics. The heat from deep inside the planet causes the mantle to move, which is why continents shift, and earthquakes and volcanoes happen.Science and Engineering Practice (SEP): Constructing...

Magnetic Polarity Evidence for Continental DriftOne of the most substantial pieces of evidence supporting continental drift and plate tectonics comes from Earth’s magnetic field. Over millions of years, Earth’s magnetic polarity has reversed many times, meaning the north and south magnetic poles have switched places. When molten rock cools and solidifies at mid-ocean ridges, the magnetic minerals inside align with Earth's magnetic field at that time. This creates striped patterns on the...

Magma CompositionMagma is molten rock beneath the Earth's surface. When it erupts from a volcano, it is called lava. The composition of magma determines how a volcano erupts. Different types of magma contain varying amounts of silica, gas content, and temperature, which influence how thick or fluid the magma is. Science and Engineering Practice (SEP): Constructing Explanations and Designing SolutionsScientists construct scientific explanations about magma composition using multiple sources of...

Bathymetric Evidence for Seafloor SpreadingThe ocean floor is not flat it has mountains, valleys, and ridges that provide clues about how Earth’s surface changes. Bathymetry is the study of the ocean floor’s depth and shape. Scientists have used sonar and satellite imaging to map the ocean floor, revealing mid-ocean ridges, deep trenches, and rift valleys. These features provide strong evidence for seafloor spreading, a process where new oceanic crust forms at mid-ocean ridges and moves...