lesson 17/18/19: sedimentary rocks, types, metamorphic rocks

Question 1

limestone

Answer 1

is a sedimentary rock that is formed from the deposits of the remains of sea organisms such as algae, brachiopods and carls. The remains of some of these organisms are still visible within limestone, while others are microscopic. The skeletal hard parts of these dead animals contain calcium carbonate. When the organisms die, fragments of their skeleton deposit as sediments and cemented together over a period of time

Question 2

coal

Answer 2

is a sedimentary rock formed from the remains of dead plants that are buried by other sediments. In dense swamps, layers of dead trees and other plants build up on the wet floor. If these layers are covered with water before rotting is completed, they can bury other sediments. The weight of the sediments above compacts the partially decayed plant mineral. Over millions of years the compaction and heating squeeze out the water forming coal.

Question 3

law of superposition and index fossils

Answer 3

• Geologic timescale breaks up the Earth’s history into eras and ions
• Geologists look for clues in sedimentary rock layers
• Look at the mineral composition for asteroids for volcanoes
• Fossil records for animals
• Unless the layers are disturbed or turned over, the layers at the bottom are always older than the layers at the top
• This process is called relative dating, showing who came first
• Igneous intrusion - formed from molten rock that cooled. The law of superposition does not work
• Law of crosscutting relationships when two geologic feature cross or intersect, the feature that cuts through the other is youngest
• Fossils also help with finding the relative age of a rock
• The geologic time scale helps demonstrate the order in which fossils and major geological events happened, and how it shaped the Earth into what it is today.

Question 4

EXPLAIN HOW INDEX FOSSILS SUPPORT THE LAW OF SUPERPOSITION BY ENABLING RELATIVE DATING OF SEDIMENTARY ROCKS

Answer 4

Index fossils support the law of superposition by enabling relative dating to be used in sedimentary rocks. Sedimentary rocks are made up of many , many layers that have been created over a very long period of time. Each different layer was made at in a different time period, and if these layers contain a fossil of a plant or animal (index fossils) it will show when these things existed. For example, if the first human remains are thought to be 200,00 years old, and then they were found in a rock, enabling relative dating this rock cannot be older than 200,000 years.