Question

early oceans forming what happened during the event, which tectonic plates were involved, and how it changed earth's surface.

Answer 1

Short answer
- The “early oceans forming” was not a single instantaneous event but a sequence beginning as the hot, volatile-rich young Earth cooled: steam in the atmosphere condensed into liquid water, supplemented by water delivered by comets and hydrated minerals. That produced the first global surface oceans by roughly 4.4–3.8 billion years ago (Ga).
- There were no modern tectonic plates then. Tectonics was in a proto-plate regime (small microplates, episodic subduction or vertical tectonics), and the earliest subduction and crust-forming processes helped create and stabilize the first continental blocks (cratons).
- The arrival of liquid oceans fundamentally changed Earth’s surface and systems: it enabled chemical weathering and sedimentation, altered heat and volatile cycles (including the carbon cycle), helped produce continental crust, and set the stage for the origin and evolution of life.

What happened — key steps and timing
- Very early Earth (~4.6–4.4 Ga): after accretion and the Moon-forming giant impact the surface cooled from a magma ocean. The young atmosphere was rich in H2O, CO2, N2 and other volatiles from outgassing of the mantle.
- Condensation of water (~4.4–3.8 Ga): as surface temperatures fell, atmospheric steam condensed to liquid water and pooled into basins; ancient zircon minerals (oxygen isotopes) dated to ≈4.4 Ga indicate liquid water and relatively cool crust existed by then. Intermittent heavy impacts (Late Heavy Bombardment proposed ~4.1–3.8 Ga) may have episodically boiled away and then reformed oceans.
- Continued delivery and recycling: some water likely arrived later via volatile-rich asteroids and comets; water became stored in ocean basins, sediments, hydrated minerals and the mantle.

Which “plates” were involved
- No modern plates: the familiar global plate mosaic (Pacific, North American, African, etc.) did not exist. Instead the early lithosphere was likely broken into small proto-plates, microcontinents and mobile belts.
- Evidence for early plate-like behavior: Archean greenstone belts, high-pressure metamorphic rocks and paired metamorphic belts suggest localized subduction and horizontal plate motion as early as the Archean (≈3.5–3.0 Ga) and possibly episodically earlier.
- Key point: the oceans themselves promoted tectonics (see below), but the tectonic regime was different — likely more episodic, with switching between stagnant-lid, plume-dominated and early plate-like behaviors. The specific “plates” are unknown and not the modern plates.

How the formation of oceans changed Earth’s surface and systems
- Surface morphology and sedimentation
- Creation of continental shelves and large marine basins where sediments could accumulate (sandstones, shales, carbonates).
- Formation and burial of marine chemical sediments including banded iron formations (BIFs) in the Archean and early Proterozoic, which record ocean chemistry and later oxygenation events.
- Chemical weathering and the carbon cycle
- Liquid water enabled silicate weathering, drawing CO2 from the atmosphere and regulating climate (the long-term carbon–silicate cycle). This helped stabilize surface temperatures over geologic time.
- Continental growth and crust evolution
- Water lowers the melting point of mantle rocks and facilitates partial melting, so the presence of water helped produce and differentiate continental crust. Subduction (even if intermittent) recycled crust and grew cratons.
- Influence on tectonics
- Water weakens lithospheric rocks and lubricates faults, encouraging plate motion and subduction—so the oceans themselves fed back to promote more active tectonics.
- Climate and habitability
- Oceans moderated global temperature (higher heat capacity than atmosphere) and provided environments for prebiotic chemistry and early life. Ocean chemistry (availability of dissolved ions, redox state) governed niches for early microbial ecosystems.
- Surface albedo and erosion
- Oceans changed planetary albedo and became the main agents of erosion and sediment transport, reshaping the surface through fluvial and marine processes.

Uncertainties and debates
- Exact timing: mineral evidence (old zircons) implies liquid water by ≈4.4 Ga, but continuous global oceans may have been reestablished only after episodic impact sterilizations.
- Tectonic regime: whether modern-style plate tectonics began in the Hadean, early Archean, or much later is debated; many researchers favor an early, different style of plate behavior (small plates, intermittent subduction).
- Source of water: relative importance of nebular capture, endogenous outgassing, hydrated planetesimals, and late delivery by comets/asteroids is still being quantified.

If you want, I can
- Sketch a simple timeline with major lines of evidence (zircons, BIFs, LHB), or
- Summarize how ocean formation influenced the origin of life and the first biosignatures.