Putting Dates to the Past (01:28)

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Scientists have been able to answer many questions about the Earth’s history thanks to meticulous study of rocks and fossils. Dating methods allow them to put dates to human history, the story of life, and the past of Earth.

History (03:55)

The origins of the Earth and life fascinate humankind; religions monopolized answers for many years. Geological findings help scientists date the Earth.

Relative Dating Methods (01:51)

These methods compare different remains and objects to determine which are older and which share common periods of time. Stratigraphy is the science of studying sediments that, over time, form stratified layers. Each layer contains characteristic fossils, allowing scientists to divide the age of the Earth into four main eras: the Precambrian Era, the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era.

Absolute Dating Techniques (01:29)

The methods that provide more specific dates include the study of the growth tree rings; the study of air bubbles trapped in Antarctic ice; and the study of glacial sediment deposits. The most important methods are based on radioactivity.

Radioactive Absolute Dating: Carbon-14 (04:04)

In any sample of radioactive material, its half-life is the time it takes for half the sample to decay. The half-life of carbon-14 is 5,730 years. Scientists can study its concentration in animal and plant remains to precisely determine the time of death.

Delicacy of a Footprint (03:14)

The oldest known hominid footprints, left by a male and female, were discovered in Tanzania in 1979. Scientists determined the height, weight of the pair and the speed at which they traveled 3.6 million years ago.

Summary (03:15)

This segment reviews the concepts of dating the past discussed in this video.

Credits: Putting Dates to the Past (02:15)

Credits: Putting Dates to the Past