MTTC Earth/Space Science (020) common mistakes
MTTC Earth/Space Science (020) · Understand the traps and how to avoid them.
When a stem asks which layer of Earth is liquid, answering 'the asthenosphere' because it is described as plastic or partially molten, rather than identifying the outer core as the only fully liquid layer.
Review courses emphasize the asthenosphere's role in plate tectonics and isostatic adjustment, so 'partially molten' gets misread as 'liquid'; seismic evidence (S-wave shadow zone) that distinguishes a true liquid from a ductile solid is often studied separately and never connected to the layer question.
What to do instead
Build a one-page layer table with composition, physical state, depth range, and the single piece of evidence for each (S-wave shadow zone for the outer core, P- and S-wave velocity jump at the Moho, brittle-versus-ductile behavior for the lithosphere/asthenosphere boundary). Practice explaining why S-waves cannot travel through the outer core but can travel through the asthenosphere.
Treating the rock cycle as a fixed sequence (igneous to sedimentary to metamorphic) and misclassifying rocks that skip steps, such as a quartzite formed directly from a quartz sandstone or an igneous rock that becomes sedimentary without a metamorphic stage.
Textbook diagrams are drawn as closed loops with arrows in one direction, which creates a memorized order; candidates then answer classification items by position in the loop instead of by texture, mineralogy, and formation process.
What to do instead
Classify every rock by observable criteria first: grain size and sorting, foliation, mineral assemblage, and cooling history (phaneritic versus aphanitic, intrusive versus extrusive). Practice with specific examples that break the loop, such as obsidian, conglomerate, and quartzite, and state the process that formed each one.
Explaining seasons by Earth's changing distance from the Sun, or by the tilt causing one hemisphere to be 'closer' to the Sun, instead of by the changing angle of incoming sunlight and day length caused by a constant axial tilt.
The elliptical orbit and perihelion in January are memorable facts, and diagrams of a tilted globe make 'closer to the Sun' feel visually plausible; the misconception survives because it is rarely tested against a counterexample.
What to do instead
Memorize two disconfirming facts and use them in explanations: perihelion occurs during Northern Hemisphere winter, and the two hemispheres have opposite seasons simultaneously. Then explain the mechanism in terms of solar elevation angle, insolation intensity, and daylight duration at a given latitude.
Confusing the cause of the tides with the cause of the seasons, or stating that the Moon's gravity alone produces tides without accounting for the differential gravitational pull across Earth's diameter and the Sun's contribution.
Both topics involve the Sun, the Moon, and Earth's orientation, and both are taught with simplified diagrams; candidates memorize 'the Moon causes tides' as a slogan and cannot explain spring versus neap tides quantitatively.
What to do instead
Write out the tidal mechanism explicitly: the inverse-square falloff of lunar gravity across Earth's diameter produces two bulges, and the Sun contributes roughly half the lunar tidal force. Then predict spring and neap tides from the alignment of Sun, Earth, and Moon at new, full, and quarter phases.
Reading a topographic map or a cross-section and reporting the direction of groundwater flow or river flow without checking contour spacing, V-rule geometry, and elevation labels, so flow direction is reversed or gradients are misjudged.
Candidates rely on the visual impression of an arrow or a shaded band rather than applying the rules; contour intervals and the meaning of closely spaced contours are recalled as definitions but not applied under time pressure.
What to do instead
Practice a fixed routine: identify the contour interval, locate index contours, apply the V-rule (contours point upstream), and compute gradient as elevation change divided by horizontal distance using the map scale. Do several items where the correct answer requires reversing an intuitive guess.
Designing an 'experiment' for an inquiry item that has no control, no manipulated variable, or no measurable outcome, and calling it valid because it is hands-on.
Candidates equate student engagement with scientific validity and have practiced writing engaging activities more than writing testable designs; the items reward identifying variables over describing procedures.
What to do instead
For every proposed investigation, state the independent variable, dependent variable, at least one controlled variable, and the data that would be collected. Reject designs in which two variables change at once or in which the outcome is an opinion rather than a measurement.
Treating a hypothesis as a guess and a theory as a tentative idea, so items about the nature of science and the status of plate tectonics or evolution are answered with 'just a theory' reasoning.
Everyday English usage of 'theory' conflicts with the scientific meaning, and candidates do not distinguish hypothesis, law, and theory as different kinds of knowledge claims rather than points on a ladder of certainty.
What to do instead
Learn the operational definitions: a hypothesis is a testable prediction, a law describes a consistent relationship, and a theory is a well-substantiated explanatory framework supported by multiple independent lines of evidence. Practice explaining what evidence would count against a theory, which is the mark of scientific status.
Solving a radioactive-decay or half-life item by dividing the age by the half-life and stopping there, instead of converting the remaining parent fraction into a number of half-lives before computing age.
The formula is remembered as 'age equals half-life times something' without the logarithmic step, and the arithmetic is done quickly under time pressure with no check that the remaining fraction is consistent with the computed age.
What to do instead
Use a table of remaining parent fraction after 0, 1, 2, 3, and 4 half-lives (100, 50, 25, 12.5, 6.25 percent) and work backward from the stated fraction. Always verify by checking that the age is plausible relative to the half-life and that parent plus daughter equals 100 percent.
Selecting an assessment or instructional strategy for a constructed-response item without aligning it to the stated learning objective, so a question that asks students to analyze data is graded with a recall-level rubric.
Candidates answer from general preference ('I like labs' or 'I like multiple choice') rather than mapping the verb in the objective to the cognitive demand of the task and the rubric; alignment is studied as a concept but not practiced as a matching exercise.
What to do instead
Practice a three-column alignment drill: objective verb, task type, and rubric criterion. Match analyze and evaluate objectives to data-interpretation tasks with scoring criteria about reasoning and evidence, and match recall objectives to selected-response items. Check that the rubric describes the same behavior the objective names.
Ignoring the difference between a misconception and a random error when interpreting student responses, and planning reteaching that repeats the original explanation louder instead of confronting the specific incorrect model.
Candidates diagnose wrong answers as 'didn't study' and default to re-lecturing; identifying the underlying mental model requires knowing the common alternative conceptions in Earth and space science and asking a follow-up question to surface them.
What to do instead
Learn the standard alternative conceptions for each topic (distance-cause seasons, Moon phases caused by Earth's shadow, tides caused by the Moon only) and prepare a diagnostic question and a discrepant-event demonstration for each. When a student errs, ask them to explain their reasoning before choosing a reteaching strategy.