If the same species of reptile was found in Africa and south america, what could this evidence support? Played times. Print Share Edit Delete. Live Game Live. Finish Editing.
Why are no fossils found in precambrian rocks? | Yahoo Answers
Geologists count back more than 4 billion years to the oldest Earth materials. Have you ever tried to count to a million? Counting once per second easy at the start, but tough when you reach the hundred-thousand mark , 24 hours per day, seven days per week no weekends off , it would take you 11 days, 14 hours to count to one million! There are a thousand millions in a billion, so counting to a billion would take you approximately 32 years. Taking this one step further, it is not humanly possible to count to 4. To help comprehend the length of geologic time, some analogies are provided below. Select an analogy:.
Telling Time at Grand Canyon National Park
Stratigraphy is the study of rock layers strata deposited in the earth. It is one of the most challenging of geologic subdisciplines, comparable to an exacting form of detective work, yet it is also one of the most important branches of study in the geologic sciences. Earth 's history, quite literally, is written on the strata of its rocks, and from observing these layers, geologists have been able to form an idea of the various phases in that long history.
Slowly and painstakingly, geologists have assembled this record into the generalized geologic time scale shown in Figure 1. This was done by observing the relative age sequence of rock units in a given area and determining, from stratigraphic relations, which rock units are younger, which are older, and what assemblages of fossils are contained in each unit. Using fossils to correlate from area to area, geologists have been able to work out a relative worldwide order of rock formations and to divide the rock record and geologic time into the eras, periods, and epochs shown in Figure 1. The last modification to the geologic time scale of Figure 1 was in the s, before radiometric dating was fully developed, when the Oligocene Epoch was inserted between the Eocene and the Miocene. Although early stratigraphers could determine the relative order of rock units and fossils, they could only estimate the lengths of time involved by observing the rates of present geologic processes and comparing the rocks produced by those processes with those preserved in the stratigraphic record.