Cretaceous_E

 Copilot:

If all the ice currently covering the planet were to melt, how much land would be left? Is Earth basically a water planet?

Short answer

If all land-based ice on Earth melted, global sea level would rise on the order of 60–70 meters. 

Land left: The vast majority of continents sit well above 70 m, so most land would still be there. You’d lose today’s low-lying coasts, river deltas, and many coastal plains, but probably on the order of only a few to maybe 10 percent of current land area would be submerged—not half the continents or anything close.

Surface balance: Right now, Earth is about 71% ocean, 29% land. With a 60–70 m rise, oceans would cover more area and land would shrink somewhat, so you’d be looking at something like roughly three-quarters ocean, one-quarter land (exact numbers depend on detailed topography, but that’s the ballpark).

So…is Earth basically a water planet?

Yes—even in this extreme “all ice melted” scenario, Earth is still dominantly an ocean world by surface area, just a slightly more ocean-heavy one than today. The continents don’t vanish; their shapes and coastlines change dramatically, but large interior regions of North America, South America, Africa, Eurasia, and Australia remain above sea level.

If you want, we can zoom in on a specific region—like Quebec or North America—and talk through what that 60–70 m world would actually look like on the ground.

Does Earth loose much water to outer space over time. Clearly, this is more land than earlier epochs enjoyed...

Earth does lose water to space, but the rate is so small that it barely affects the total ocean volume over geological time. The interesting twist is that Earth’s land area has changed far more because of plate tectonics and continental configuration than because of water loss.

🌍 How much water does Earth actually lose?

Two main escape pathways matter:

1. Hydrogen escape from the upper atmosphere

UV light splits water vapor high in the atmosphere.

The hydrogen escapes to space because it’s extremely light.

Modern estimates put this loss at roughly 1–3 kg of hydrogen per second, which corresponds to about 1–2 liters of water per second once you account for oxygen.

Over a billion years, that adds up to only a few centimeters of ocean depth.

2. Ionospheric escape (oxygen and hydrogen ions)

Solar wind strips ions from the upper atmosphere.

Earth’s magnetic field reduces this loss dramatically compared to Mars or Venus.

Bottom line:

Earth loses water, but so slowly that it would take tens of billions of years to noticeably shrink the oceans—longer than the Sun’s remaining lifetime.

🌊 So why does Earth have more exposed land now than in earlier epochs?

You’re absolutely right: earlier Earth epochs—especially the mid‑Cretaceous and early Paleozoic—had less exposed land and higher sea levels. But this wasn’t because Earth had more water.

The real drivers were:

1. Faster seafloor spreading

Hotter mantle → more buoyant mid‑ocean ridges → ocean basins become shallower.

Shallower basins hold less water → sea level rises globally.

2. No large continental ice sheets

When Antarctica and Greenland weren’t glaciated, all that water was in the oceans.

3. Thermal expansion of seawater

Warmer global temperatures expand ocean volume.

4. Continental arrangement

Supercontinents like Pangaea create large interior basins.

Fragmented continents create more shallow continental shelves.

Result:

During the Cretaceous, sea level was 150–250 m higher than today. Vast areas of what is now land—including much of the U.S. Midwest, Europe, and parts of Africa—were underwater.

This had nothing to do with Earth having more water; it was about how much room the ocean basins had to store it.

🧭 Putting it together

Water loss to space: real but negligible.

Land exposure over time: controlled by tectonics, mantle temperature, and glaciation cycles—not by total water inventory.

Earth today: has more exposed land than many past epochs because ocean basins are deeper and large ice sheets lock up water.

If you want, we can map how Quebec or North America looked during high‑sea‑level epochs like the Cretaceous—it’s a fun comparison to the “all ice melted” scenario you asked about earlier.

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https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event