how does rock sequences help me Understand the earth Distant past?
Answers
Answer:
The location of fossils in rock layers provides evidence of Earth's past landscapes. It is hard to guess the age of rock. Scientists have to act like detectives, piecing together a mystery to determine how long ago rocks formed. Fossils found in a particular rock layer help scientists determine the age of the rock.
Answer:
The Earth is dynamic, consisting of constantly moving plates that are made of rigid continental and oceanic lithosphere overlying a churning, plastically flowing asthenosphere (Figure 1.1). These plates pull apart, collide, or slide past one another with great force, creating strings of volcanic islands, new ocean floor, earthquakes, and mountains. The continents likewise continuously shift position because they are part of the moving plates. This not only shapes the land over time, but it also affects the distribution of rocks and minerals, natural resources, climate, and life.
Reconstructing the past is a lot like solving a mystery. Geologists use scraps of evidence to piece together events they have not personally observed, but to do so they must contend with two major complications. First, the overwhelming majority of geologic history occurred long before there were any human witnesses. Second, much of the evidence for the older events is highly fragmented.
See Chapter 2: Rocks to learn more about different rocks found in the West.
Rocks and sediments are indicators of past geologic processes and the environments in which those processes took place. In general, igneous rocks, created through tectonic activity, reflect past volcanism. By looking at both their texture and chemistry we can determine the tectonic setting and whether or not the rocks formed at the surface or deep underground. Likewise, metamorphic rocks, created when sediment is subjected to intense heat and pressure, provide important clues of past mountain-building events, and geologists often use them to map the extent of now-vanished mountain ranges. Sedimentary rocks tell perhaps the most comprehensive story of the Earth’s history, as they record characteristics of far-away mountain ranges, river systems that transported the sediments, and the final environment in which the sediments accumulated and lithified. The size and shape of sediments in sedimentary rocks, as well as the presence of fossils and the architecture of sedimentary rock layers (sedimentary structures), can help us infer how the sediments were transported and where they were finally deposited. However, because rocks are often reformed into different rock types, ancient information is lost as the rocks cycle through the igneous, metamorphic, and sedimentary stages.
See Chapter 3: Fossils for more information about the West’s prehistoric life.
Fossils indicate both the type of life that once flourished in an area and the kind of climate in which that life existed. Paleontologists use groups of fossils found in the same place to construct pictures of entire ecosystems. These ecosystems of the past are matched to similar present-day ecosystems, whose climate conditions are then used to infer what sort of climate the fossilized organisms lived in. Unfortunately, few organisms are easily preserved as fossils, and many environments also do not lend themselves to preserving organisms as fossils. As a result, the clues that fossils give provide only glimpses of the ancient world, with many important details missing.