What is Earth made of inside, and what evidence shows the plates move?
Describe the layered structure of Earth's interior and explain the theory of plate tectonics, including the evidence (sea-floor spreading, matching coastlines, fossils, magnetic stripes) and the calculation of plate spreading rate.
A Regents answer on Earth's interior and plate tectonics: the crust, mantle, outer and inner core and the Reference Tables inferred properties, mantle convection as the driver, the three boundary types, the evidence for sea-floor spreading (matching coastlines, fossils, magnetic stripes, age of sea floor), and a worked spreading-rate calculation.
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What this topic is asking
The Regents wants you to describe the layered interior of Earth (using the Inferred Properties of Earth's Interior page) and to explain plate tectonics: the boundary types, the driver (mantle convection), and the evidence for moving plates, including a spreading-rate calculation with the rate-of-change equation.
Earth's layered interior
The Reference Tables Inferred Properties of Earth's Interior page shows that temperature, pressure and density all increase with depth. It also marks the Moho (the crust-mantle boundary) and the depths of the major layers. A classic data-reading task: use the graph to state the temperature or density at a given depth, or to identify which layer is liquid (the outer core, where the S-wave shadow zone shows S-waves cannot pass through it).
What drives plate motion
The three boundary types
- Divergent: plates move apart; magma rises to form new oceanic crust at mid-ocean ridges (the Mid-Atlantic Ridge), or rift valleys on land.
- Convergent: plates collide; denser oceanic crust subducts, building deep-ocean trenches, volcanoes and mountains and causing large earthquakes.
- Transform: plates slide past each other along faults (the San Andreas Fault), causing earthquakes but neither creating nor destroying crust.
The evidence for plate tectonics
- Matching coastlines of continents (South America and Africa fit like puzzle pieces).
- Matching fossils and rock types on continents now separated by oceans.
- Sea-floor spreading: at mid-ocean ridges new crust forms, so the sea floor is youngest at the ridge and progressively older away from it.
- Symmetric magnetic stripes: as new crust cools, it records Earth's magnetic field; reversals produce mirror-image stripes on both sides of the ridge, proving the sea floor spread outward.
Calculating the spreading rate
The Reference Tables rate-of-change equation gives the spreading rate:
Try this
Q1. State what drives the movement of Earth's plates. [1 point]
- Cue. Convection currents in the mantle, powered by Earth's internal heat.
Q2. Explain how symmetric magnetic stripes on the sea floor support sea-floor spreading. [2 points]
- Cue. New crust forms at the ridge and records the magnetic field as it cools; field reversals create mirror-image stripes on both sides, showing crust moved outward symmetrically.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)2 marksPart B-2. New oceanic crust forms at a mid-ocean ridge. Identical magnetic stripe patterns are found at equal distances on both sides of the ridge, and matching rock is now 1,200 km from the ridge after 60 million years. Calculate the average rate of sea-floor spreading on one side of the ridge in centimeters per year. Show the equation, the substitution and the answer with units.Show worked answer →
A 2-point calculation using the rate-of-change equation.
1 point for the correct setup and substitution, 1 point for the correct answer with units.
Equation (rate of change): rate = change in distance / time.
Convert: 1,200 km = 120,000,000 cm; 60 million years = 60,000,000 years.
Substitution: rate = 120,000,000 cm / 60,000,000 years.
Answer: 2 cm/year.
Markers reward the equation, a correct unit conversion, and 2 cm/year. A common error is forgetting to convert km to cm or using both sides (2,400 km) instead of one side.
Regents (style)1 marksPart A. The Reference Tables show that the boundary between the crust and the mantle is the (1) inner core (2) Moho (3) asthenosphere (4) lithosphere. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (2).
The Moho (Mohorovicic discontinuity) is the boundary between the crust and the mantle, shown on the Inferred Properties of Earth's Interior page. The inner core (1) is the solid center; the asthenosphere (3) is the plastic upper-mantle layer the plates ride on; the lithosphere (4) is the rigid crust-plus-upper-mantle layer that makes up the plates. The trap is confusing the lithosphere (a layer) with the Moho (a boundary).
Related dot points
- Describe the rock cycle and explain how igneous rocks form from cooling magma or lava, using the Reference Tables Scheme for Igneous Rock Identification to relate texture, composition, color and density to the rock name.
A Regents answer on the rock cycle and igneous rocks: the three rock families and the processes that link them, how cooling rate controls crystal (grain) size, how the Scheme for Igneous Rock Identification relates texture, mineral composition, color and density to a rock name (granite, basalt, obsidian and others), with worked exam questions.
- Explain how P-waves and S-waves behave and use the Reference Tables earthquake travel-time graph to find the distance to an epicenter, the origin time and the number of stations needed to locate it.
A Regents answer on earthquakes and seismic waves: P-waves and S-waves and how they differ, the Reference Tables P-wave and S-wave travel-time graph, finding the distance to an epicenter from the S-minus-P time, finding the origin time, why three stations are needed, and how the S-wave shadow zone reveals a liquid outer core, with worked exam questions.
- Explain where and why volcanoes form (boundaries and hot spots), describe how crustal rock is deformed by folding, faulting and tilting, and interpret evidence of crustal movement such as displaced rock layers and marine fossils on mountains.
A Regents answer on volcanoes and crustal deformation: why volcanoes form at subduction zones, divergent boundaries and hot spots, the Ring of Fire, how rock is folded, faulted and tilted, and the evidence that the crust has moved (displaced strata, tilted layers, marine fossils and rounded sediments now on mountains), with worked exam questions.
- Use the Reference Tables Geologic History of New York State and the bedrock map to read New York's tectonic and environmental history, including ancient mountain-building, shallow seas and the most recent glaciation.
A Regents answer on New York's geologic history: how to read the Geologic History of New York State chart and the bedrock map together, the ancient mountain-building (orogenies), the shallow seas that left marine fossils and sedimentary rock, the oldest Precambrian rock of the Adirondacks, and the last ice age that shaped today's landscape, with worked exam questions.
- Calculate the eccentricity of an elliptical orbit using the Reference Tables equation (distance between foci divided by length of the major axis) and relate eccentricity to orbital shape and orbital velocity.
A Regents answer on orbital eccentricity: ellipses and foci, the Reference Tables formula (distance between foci over the length of the major axis), worked calculations rounded to the nearest thousandth, and how eccentricity and the Sun's off-center position affect orbital velocity and apparent solar diameter.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)