Earth Science

The crust is the outermost layer of the Earth. It varies in thickness from about 3 miles under the oceans to about 25 miles under the continents.

Igneous rocks are formed when magma (underground) or lava (on the surface) cools and solidifies. Common examples include granite and basalt.

The Richter scale (developed by Charles Richter in 1935) measures earthquake magnitude. Today, scientists more commonly use the moment magnitude scale, but 'Richter scale' remains the widely known term.

Approximately 71% of the Earth's surface is covered by water. The oceans hold about 96.5% of all Earth's water, with the Pacific Ocean being the largest.

The Beaufort scale measures wind speed and was developed in 1805 by Sir Francis Beaufort of the Royal Navy. It ranges from 0 (calm) to 12 (hurricane force).

Pangaea was the supercontinent that existed during the late Paleozoic and early Mesozoic eras. It began to break apart about 175 million years ago, eventually forming the continents we know today.

Diamond is the hardest known natural mineral, rated 10 on the Mohs hardness scale. It is made of pure carbon arranged in a crystal structure and can only be scratched by another diamond.

Tides are primarily caused by the gravitational pull of the Moon, with a smaller contribution from the Sun. When the Moon and Sun align, they produce larger 'spring tides'; when at right angles, smaller 'neap tides.'

The Ring of Fire encircles the Pacific Ocean, stretching from New Zealand along the eastern edge of Asia, north across the Aleutian Islands, and south along the west coast of the Americas. It contains about 75% of the world's active volcanoes.

Cumulonimbus clouds are massive, towering clouds associated with thunderstorms, heavy rain, hail, lightning, and even tornadoes. They can extend from near ground level to over 40,000 feet in altitude.

The epicenter is the point on the Earth's surface directly above the focus (or hypocenter), which is where the earthquake actually begins underground. The epicenter is typically where the strongest shaking is felt.

The Himalayas were formed by the collision of the Indian tectonic plate with the Eurasian plate, which began about 50 million years ago. The mountains are still rising by about 5 mm per year.

The Mohorovicic discontinuity (Moho) is the boundary between the Earth's crust and the mantle. Discovered by Croatian seismologist Andrija Mohorovicic in 1909, it is identified by a change in seismic wave velocity.

Geomagnetic reversal is the phenomenon where the Earth's magnetic north and south poles switch places. This has happened hundreds of times over Earth's history, with the last reversal occurring about 780,000 years ago.

The Earth is approximately 4.5 billion years old (4.54 billion to be more precise), based on radiometric dating of meteorites and the oldest known rocks and minerals on Earth.