Tag: science & technology

The nebular theory (also called nebular hypothesis) explains that the solar system formed from a rotating cloud of gas and dust (nebula) that condensed under gravity. While 'gravitational condensation theory' isn't the standard scientific name (the correct term is nebular theory), the answer key intends this option as it's the only one describing condensation from gases and dust particles over time. The other options are not real scientific theories.

The air we breathe is approximately 78% nitrogen, 21% oxygen, and 1% other gases (argon, carbon dioxide, etc.). So nitrogen is the most common gas, making oxygen the second most common. Carbon dioxide, while important for climate, makes up only about 0.04% of the atmosphere.

The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions, covering about 63 million square miles (165 million square kilometers) - more than the entire land area of Earth. It extends from the Arctic in the north to the Antarctic in the south. The Indian Ocean is third largest, and the Bay of Bengal is part of the Indian Ocean.

Earth is the third planet from the sun (after Mercury and Venus) and the fifth largest by diameter (after Jupiter, Saturn, Uranus, and Neptune). The order from the sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Earth is the largest of the terrestrial (rocky) planets but smaller than the gas giants.

Earth is spherical due to gravity, which pulls all matter toward the center of mass. During Earth's formation, the molten material was pulled equally inward in all directions by gravitational force, naturally forming a sphere (the shape with minimum surface area for a given volume. This is why all large bodies in space (planets, stars) are spherical. Magnetism attracts only certain materials, and heat would cause expansion, not spherical shaping.

The atmosphere is the layer of gases surrounding Earth, held in place by gravity. It's primarily nitrogen (78%) and oxygen (21%), with trace amounts of other gases. Photosphere and chromosphere are layers of the sun, not Earth. The atmosphere protects life by absorbing UV radiation, regulating temperature, and providing the air we breathe.

Earth's axial tilt (approximately 23.5 degrees from vertical) causes the seasons because different parts of Earth receive varying amounts of sunlight throughout the year as it orbits the sun. When the Northern Hemisphere tilts toward the sun, it's summer there (and winter in the Southern Hemisphere). Six months later, the situation reverses. Meteor showers and solar wind are unrelated phenomena.

Day and night are caused by Earth's rotation on its axis. As Earth spins, different parts face the sun (daylight) or face away (nighttime). One complete rotation takes about 24 hours. Revolution refers to Earth's year-long orbit around the sun, not the daily cycle of day and night. 'Evolution' is a biological process unrelated to Earth's movements.

Earth's revolution is its year-long journey around the sun, taking approximately 365 days. Rotation refers to Earth spinning on its own axis every 24 hours, which causes day and night, not the annual orbit.