Geo 103 Midterm1

Latitude

Angular distance north or south of the equator. Latitude lines are called parallels and run east-west from 0° at the equator to 90° at each pole.

Northern Hemisphere

Locations with latitudes from 0° to 90° N.

Southern Hemisphere

Locations with latitudes from 0° to 90° S.

Latitude distance conversions

1° of latitude = 60 nautical miles. 1 minute of latitude = 1 nautical mile. 1 nautical mile = approximately 1.15 regular miles.

Longitude

Angular distance east or west of the Prime Meridian. Longitude lines are called meridians and run north-south.

Prime Meridian

The 0° longitude line passing through Greenwich, England.

Eastern and Western Hemispheres

Locations east of Greenwich are 0° to 180° E. Locations west of Greenwich are 0° to 180° W.

Earth’s rotation

Earth rotates eastward through 360° in 24 hours.

Longitude and time conversion

Earth rotates 15° per hour because 360° ÷ 24 hours = 15° per hour.

How to calculate longitude from time difference

Longitude = time difference from Greenwich × 15° per hour.

Determining east versus west longitude

If local noon occurs before noon at Greenwich, the location is ahead and east. If Greenwich has already passed noon when local noon occurs, the location is behind and west.

Finding latitude using Polaris

In the Northern Hemisphere, the angle between Polaris and the horizon approximately equals the observer’s latitude.

Navigation example: Polaris is 21° above the horizon and local noon occurs at 10:30 PM GMT

Latitude = 21° N. The 10.5-hour difference means the location is behind Greenwich, so longitude = 10.5 × 15° = 157.5° W or 157°30′ W.

Piloting

Navigating by using visible landmarks, especially along coastlines.

Dead reckoning

Estimating current position from a previous known position using speed, elapsed time, and direction. Errors accumulate over time.

Chronometer

A sea-worthy accurate clock invented by John Harrison that allowed navigators to compare local noon with Greenwich time and calculate longitude.

Bathymetry

The measurement and mapping of the depth and relief of the seafloor.

Soundings

Early depth measurements made by lowering weighted leadlines from ships. They were slow, sparse, and less accurate in deep water.

Bathymetric map

A map showing the depth and relief of the seafloor.

Isobaths

Lines on a bathymetric map connecting points of equal water depth.

Interpreting isobath spacing

Closely spaced isobaths indicate a steep slope. Widely spaced isobaths indicate a gentle or flat area.

Major continental-margin features in order

Continental shelf → continental slope → continental rise → abyssal plain.

Echo sounder

A ship-based instrument that sends high-frequency sound waves toward the seafloor and records their return with a hydrophone.

What does single-beam echo sounding produce?

A continuous two-dimensional depth profile along the ship’s path.

Echo-sounding depth formula

Depth = sound velocity × travel time ÷ 2 or d = v(t/2). Divide by 2 because the recorded time includes travel to the seafloor and back.

Speed of sound in seawater

Approximately 1,460 meters per second. In air it is approximately 343 meters per second.

Multibeam echo sounding and side-scan sonar

Send sound across a wide swath to create detailed three-dimensional maps of the seafloor. Overlapping swaths provide complete coverage.

Seismic reflection profiling

Uses lower-frequency and stronger sound energy than echo sounding to penetrate beneath the seafloor and create two-dimensional or three-dimensional images of sediment and ocean crust.

Satellite mapping of the seafloor

Satellite altimeters measure small variations in ocean-surface height caused by gravitational effects from seafloor features and differences in rock density.

Exclusive Economic Zone or EEZ

A 200-nautical-mile or approximately 370-kilometer zone in which a coastal country controls natural resources.

Three main types of seismic waves

P-waves are fast compressional waves. S-waves are slower shear waves that cannot pass through liquids. Rayleigh waves travel along Earth’s surface.

Focus

The underground point where an earthquake begins and from which seismic waves radiate.

P-wave and S-wave arrival-time difference

P-waves arrive first. A larger gap between P-wave and S-wave arrivals indicates a greater distance from the earthquake’s epicenter.

Seismic-wave refraction

P-waves and S-waves bend when they move between materials with different densities.

How seismic waves reveal Earth’s internal structure

Their refraction, arrival times, and shadow zones show that Earth consists of concentric layers with different compositions, densities, and physical states.

Evidence that the outer core is liquid

S-waves cannot travel through the outer core because S-waves cannot pass through liquids. P-wave refraction also creates a shadow zone.

Earth’s layers from outside to inside

Crust → mantle → liquid outer core → solid inner core.

Moho

The boundary between Earth’s crust and mantle.

General density pattern inside Earth

Density increases toward Earth’s center. The crust is least dense, the mantle is denser, and the iron-nickel core is densest.

Age of Earth and the Solar System

Approximately 4.56 billion years or 4.56 Ga, determined mainly through radiometric dating of meteorites and lunar samples.

Age of Earth’s oldest known rocks

Approximately 4.0 billion years.

Early Earth’s atmosphere

Produced largely by volcanic degassing and rich in CO₂, CH₄, H₂O, HCl, H₂S, and N₂, with no free oxygen.

Primary origin of Earth’s ocean water

Most surface water came from the mantle through volcanic degassing. As Earth cooled, water vapor condensed into liquid wate