EAPS 11200 Lecture 10: 02062019
19 Feb 2019
School
Department
Course
Professor
EAPS112 02062019
Absolute Time
Absolute Dating
• The determination of specific dates expressed in years before the present
• Absolute dates are obtained from natural geologic clocks such as radiometric dating.
James Hutton (1726-1797)
Lyell’s Uniformitarianism
• Only geologic processes that we observed today have acted in the past.
• Geologic processes act very slowly.
• Rates of geologic processes are constant and unchanging.
• Did not accept the possibility of global catastrophes in the history of the Earth.
Louis Agassiz (1807-1873)
• Agassiz’s recognition of past global glaciation caused the first major modification of
Lyell’s Uniformitarianism which eventually led to the development of the concept of
Actualism
Actualism
• Past geologic processes can be inferred from modern geologic processes.
• Geologic processes may have varied in rates and intensity in the past
• Some geologic processes are extremely rare and may not have been observed by
modern geologists.
• Certain geologic processes may have operated only during the very early stages of the
Earth’s history.
Lyell’s Uniformitarianism
• “...no causes whatever have from the earliest to which we can look back to the present,
ever acted, but those now acting.”
• “...they never acted with different degrees of energy from that which they now exert.”
• In essence, Lyell has described the Earth as a
• “perpetual motion machine.”
Basic Elements of the Atom
• Nucleus - is composed of protons and neutrons
• Proton - positively charged particle
• Neutron - neutrally charged particle
• Electron - negatively charged particle that revolves around the nucleus
