ASTR 1210 (O'Connell) Study Guide


12. The Earth


Earth Crescent


A. Earth as a Planet: Uniqueness


B. The Earth's Biosphere


C. The Age of the Earth

Our experience of everyday time is of little help in visualizing the age of the Earth. Hundreds or thousands of years represent the longest time scales we can easily comprehend, yet the age of the Earth is millions of times longer. The textbook-based time scale described in Study Guide 1 is probably the best way of attempting to retrain your thinking about cosmic time. Another illustration is in the form of a "cosmic clock". An example is shown at the right. At this scale, you can't even see the current era of human dominance. Click for a full-sized version.

There are two primary methods for dating the Earth's surface:

Grand Canyon

Sedimentary layers in the walls of the Grand Canyon (Reiner Stenzel). Click for cross-sectional ages.


Earth Cross-Section

Cross-section through the Earth (USGS)

D. Earth's Interior


Crustal Plates

E. "Plate Tectonics"


Atmos from Space

Earth's Atmosphere From Orbit

F. Atmosphere



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Last modified April 2017 by rwo

Drawing of seismic waves from ASTR 161 University of Tennessee. Text copyright © 1998-2017 Robert W. O'Connell. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 1210 at the University of Virginia.