Edad de la tierra (biologia)

THE AGE OF EARTH

In the past, many people believed that Earth was relatively young – just a few thousand years old. They also believed that Earth had remained unchanged over this time.

In theeighteenth and nineteenth centuries, scientists began to examine the Earth in great detail. And they offered the hypothesis that Earth was indeed very old and that it has changed over time by naturalforces like weather.

Evidence that supported the idea that earth was very old first came from the geologist James Hutton in 1788. Hutton proposed that rocks, mountain and valleys had been changedgradually by rain, heat, cold, volcano activity and other natural forces.
In1830, the geologist Charles Lyell agreed with Hutton about the Earth being old and changed.

Further evidence suggested tothem that the land is constantly moving and shifting. Forces beneath the Earth’s surface twist and bend some rock layers, bury others, and even push up some parts of the sea floor into mountainranges.

At the same time, other scientists found evidence that life on Earth had also changed over time. In stones they examined they found fossils. Fossils are the preserve remains or evidence of anancient organism.

Both geologists and biologist date the Earth’s past with the help in the rocks called the geologic time scale. That is the record of life determined by the positions of layers ofrocks.
Researches realized that fossils found in lower layers are older than the ones found in the layers above them. Relative dating is a technique used by scientists to determine the age of fossilsrelative to other fossils in different layers of rock.
Rocks are made up of many different elements. In certain rocks some of this elements are radioactive. Radioactive elements decay, or break down,into nonradioactive elements at a very steady rate. Scientists measure this rate of radioactive decay unit called a half time. A half time is the length of time required for half the radioactive...