Domain: Natural Science — Marine Science
Target concept: Salinity-driven density stratification formed by stained seawater and freshwater

Video generation prompt: A transparent glass tank, half-filled with blue-colored saltwater; clear freshwater is slowly poured from above using an inclined container.

Evaluation guide:
(i) Target concept: Density stratification driven solely by salinity-induced density difference between two miscible fluids in a quiescent tank.
Minimum mechanism: Two miscible liquids of different densities (denser blue-colored saltwater beneath, lighter clear freshwater added above) must be introduced such that the freshwater is poured gently enough that molecular diffusion has not yet blurred the boundary; the result is a sharp but metastable (not permanently immiscible) density interface, sustained by gravitational settling and the absence of turbulent mixing.
(ii)Storyline: [Phase 1] Static setup: Transparent tank with stationary blue saltwater occupying lower half (establishes baseline density layer). [Phase 2] Initiation: Inclined container enters frame above tank; clear freshwater begins flowing as a coherent, narrow stream (establishes controlled addition). [Phase 3] Interface formation: Stream contacts surface; clear liquid remains suspended without sinking; sharp horizontal boundary emerges at contact plane (confirms density-driven buoyancy arrest). [Phase 4] Sustained stratification: Boundary remains unbroken, flat, and edge-to-edge for full duration (verifies stability and absence of turbulent mixing). [Perspective constraint] Fixed frontal view showing full tank height and width; no occlusion of interface region; lighting enables unambiguous contrast between blue and clear layers.

Manual:
Experimental Procedure
1. Place a transparent glass tank on a stable surface.
2. Fill the lower half of the tank with blue-colored saltwater.
3. Hold an inclined container above the tank opening.
4. Slowly pour clear freshwater from the inclined container into the tank.
Observation of Experimental Phenomena
A sharp, horizontal interface forms and persists between the blue saltwater (below) and clear freshwater (above); no mixing or diffusion occurs across the interface during the observed period.
Summary of Experimental Principles
Salinity-driven density stratification: the denser saltwater remains beneath the lighter freshwater because of their density difference. Saltwater and freshwater are fully miscible — given enough time and turbulence they would blend — but because the freshwater is added gently and without agitation, molecular diffusion has not yet had time to blur the boundary, so a sharp, metastable interface persists over the observed timescale rather than a permanent, chemically immiscible one.

Prompt Grounding rubric:
level_1: No transparent glass tank is visible; no blue-colored saltwater is present; no clear freshwater is shown; no inclined pouring container appears; the scene does not depict this stratification demonstration at all.
level_2: A transparent container is present, but it is not half-filled with blue liquid, or the blue liquid is not confined to a lower layer; clear freshwater is present but is not shown being poured from above; the inclined container is missing; at least two of the four required elements (tank, blue saltwater, clear freshwater, inclined pouring container) are absent or misrepresented.
level_3: A transparent glass tank holds blue-colored saltwater occupying roughly the lower half, with clear liquid above it; an inclined container is visible above the tank; a pour is initiated but the stream is not clearly continuous or is not aligned with the tank opening.
level_4: The transparent glass tank is stationary and holds blue-colored saltwater in the lower half; clear freshwater is poured continuously from an inclined container held directly above the tank opening; all four required elements (tank, blue saltwater, clear freshwater, inclined container) are present and correctly identifiable, with the pour clearly directed into the tank.
level_5: The transparent glass tank is centered and fully visible, holding blue-colored saltwater that fills approximately the lower half with a sharp horizontal upper boundary; the inclined container is held steadily above the tank and pours a narrow, uninterrupted stream of clear freshwater straight down into the tank without splashing outside it; the tank, saltwater color, and inclined container keep the same appearance and relative placement for the full sequence.

Scientific and Causal Correctness rubric:
level_1: No density stratification is observed; the blue saltwater and clear freshwater appear fully mixed or homogenized; no interface between layers exists; the blue color appears uniformly dispersed through the tank or is absent; there is no visible causal link between the pouring action and any layer forming.
level_2: Two liquids are present but no stable horizontal interface forms between the saltwater and freshwater; the blue liquid rises or diffuses upward immediately upon contact; the clear liquid sinks or mixes turbulently; the interface is absent or visible for less than a second; there is no visible sign of density-driven separation between the two miscible layers.
level_3: A horizontal interface between the blue saltwater and clear freshwater appears and persists for at least 3 seconds; the blue liquid stays confined to the lower region; the clear liquid stays above without sinking; the interface is planar and mostly stable, but minor localized mixing (e.g., faint wisps of blue crossing into the clear layer near the tank walls) is visible.
level_4: A sharp, continuous, horizontal interface forms as soon as pouring begins and persists uninterrupted for the entire duration; the blue saltwater stays fully below the interface with no upward intrusion; the clear freshwater stays fully above with no downward penetration; no mixing, diffusion, or turbulence is visible anywhere along the interface.
level_5: The interface is flat and unbroken, extending edge-to-edge across the full width of the tank, with no visible haze, gradient band, or color bleed between the blue and clear layers at normal viewing distance; the blue saltwater shows no convection currents, settling motion, or shape distortion; the clear freshwater shows no downward displacement or meniscus disruption at the interface; the full causal chain is visible: pouring begins, freshwater rests atop the saltwater, the interface forms immediately, and the separation is sustained without any visible mixing.

Spatiotemporal Consistency rubric:
level_1: The tank changes position or appears in a different location mid-video; the liquid level inside the tank jumps up or down between frames with no visible pour causing it; the inclined container disappears and reappears; the lighting on the tank changes abruptly (e.g., a shadow or highlight switches side instantly); the tank walls flicker, bend, or lose transparency in patches.
level_2: The tank stays in place but visibly changes size or rotates slightly between frames; the liquid surface wobbles with no corresponding pour motion to explain it; the freshwater stream detaches from the container spout or reappears mid-air rather than flowing continuously; the shadow cast by the inclined container does not track its position; the direction of light and shadow on the tank changes from frame to frame.
level_3: The tank stays the same size, shape, and position throughout; the liquid level inside changes smoothly as the freshwater is poured, without sudden jumps; the pour stream stays connected from the container spout to the tank's liquid surface; shadows stay attached to their objects; no object flickers, warps, or breaks apart between frames.
level_4: The tank, blue saltwater layer, clear freshwater, and inclined container keep consistent size and position relative to each other throughout; the liquid level rises smoothly and only in the upper (freshwater) region as the pour continues; the pour stream stays unbroken, straight, and aligned with the tank opening; shadows from the inclined container and tank stay consistent with a single fixed light source; there is no jitter, warping, or stutter between frames.
level_5: No object's position drifts across the sequence, and the tank edges and liquid boundaries line up consistently from frame to frame; the pour stream shows no visible breaks, gaps, or splits at any point in the sequence; the saltwater-freshwater interface stays at the same height with no visible vertical drift throughout; there is no flicker in brightness or color that would make the tank, liquids, or container harder to see clearly.