Beginning of the Earth and Geologic History Geologic

Beginning of the Earth and Geologic History

Geologic History and Biological Evolution Early Earth Age of Earth • Scientists dated the oldest rock to 4 billion years old, but think the Earth formed before that • Moon formation- young Earth collided with another object, due to this Earth and moon must be similar in age Earth takes shape • Scientists think that Earth began as a ball of dust, rock and ice in space. • Gravity pulled this “junk” together • As the Earth grew larger, its gravity increased and it pulled in more and more “junk” • Due to the collision of this material, energy was released which raised Earth’s temp until it was VERY HOT. – Dense materials sank toward the bottom (hence the dense iron core), less dense, molten material hardened forming crust and mantle

Beginning of the Earth and Geologic History

Origins of Life – Theory states that volcano eruption formed the early earth’s atmosphere. – The chemical composition of the gases expelled by volcanoes makes the early gasses in the atmosphere – First organic molecules formed from inorganic substances in Earth’s early ocean, but only with a source of energy to cause such a chemical reaction to take place (solar radiation, volcanic eruptions and lighting) together with early atmospheric gases (CH 4, NH 3, H 2, N 2).

Origins of life – Earth’s early atmosphere contained no oxygen(anaerobic). – Oxygenated atmosphere started to appear as photosynthetic bacteria developed, cyanobacteria (blue-green algae).

Fossils- preserved remains or traces of living things, found in sedimentary rock **For fossil to form we the organism NEEDS to have hard parts ex. Bone, shells, teeth, seeds woody stems 1. ) The organism dies 2. ) It is buried by sediment 3. ) the sediment hardens into rock and preserves the shape of the organism 4. ) Uplift, weathering and erosion expose the fossil

Finding the Age of Rocks

Relative and Absolute Ages ¡ ¡ Relative Age The age of a rock compared to the ages of other rocks. Absolute Age The age of a rock given as the number of years since the rock formed.

Position of Rock Layers Its difficult to determine the absolute age so geologists use method to find a rock’s relative age. Use the: LAW OF SUPERPOSITION: in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

Principle of Original Horizontality- States that sediments are deposited in flat lying or horizontal layers that are parallel to the surface on which they were deposited. l. Sedimentary rocks NOT in horizontal layers have been altered after they were deposited. Anything that disturbs sedimentary rock layers, has to be YOUNGER than the layers if affects Disturbances include: l. Faulting l. Folding l. Tilting l. Igneous Intrusion or Extrusion

Clues from Igneous Rocks: Magma that cools and pushes into bodies of rock and hardens is called an Intrusion An intrusion is always younger than the rock layers around and beneath it.

The intrusion (in red) is now younger than the surrounding rocks.

Clues from Igneous Rocks: 1. Lava that hardens on the surface is called an Extrusion Rock layers below an extrusion are always older than the extrusion.

List in order the layers from oldest to youngest

List in order the layers from oldest to youngest

Clues from Faults: Fault: is a break in the Earth’s crust. • Forces inside the Earth cause movement of the rock on opposite sides of a fault. • Fault is always younger than the rock it cuts through.

Folding: • Occurs when sedimentary rock layers are bent upwards or downwards from their original horizontal position – Folding is YOUNGER than the youngest rock affected • Sometimes forces inside Earth fold layers so much that the layers are over turned – The youngest layers might end up on the bottom

GAPS IN THE GEOLOGIC RECORD - Record of sedimentary rock layers is not always complete - Deposition slowly builds layers upon layer of sedimentary rock, BUT some of these layers may erode away, exposing an older rock surface. Unconformity – is a gap in the geologic record. An unconformity shows where some rock layers have been lost because of erosion.

**It is represented by a wavy line p When rock layers erode away, an older rock surface may exposed, it may erode itself then deposition begins again building new rock layers **Due to erosion, most of the geologic rock layers and evidence in them has been lost

Geologic History and Biological Evolution List in order the layers from oldest to youngest 1. ) 2. ) 3. ) 4. ) 5. )

USING FOSSILS TO DATE ROCKS To date rock layers, geologists first give a relative age to a layer of rock at one location. THEN they can give the same age to matching layers of rock at other locations. Certain fossils, called Index Fossils help geologist match rock layers. INDEX FOSSILS – Fossils of widely distributed organisms that lived during only one short period.

• Example of an Index Fossil: • Trilobites (hard shelled animals whose bodies had distinct parts. • Trilobites evolved in shallow seas. • Over time, many types appeared. • They became extinct. • They have been found in many different places.

Absolute Age-number of years that have passed since the rock was formed. Isotope-Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes Example: Carbon-12 Carbon-14 The number after carbon indicates the mass number (protons + neutrons) for that isotope Carbon-12 Carbon-13 Carbon-14 Protons 6 6 6 Electrons 6 6 6 Neutrons 6 7 8

Radioactive Decay-the process in which the nuclei of radioactive elements break down, releasing fast moving particles and energy • During radioactive decay, the atoms of one element break down (change) to form atoms of another element. • Radioactive elements occur naturally in igneous rock • Radioactive Dating- used to determine the absolute age of rocks. By measuring the amount of radioactive isotopes in the rock!!!

Half Life-the time it takes for half of the radioactive atom to decay to the daughter element **The half life for the radioactive element never changes no matter how much the starting mass of the substance is or how much is left Determining the Absolute Age of Rocks 1. ) Scientists determine the amount of radioactive material in rock 2. ) Compare the radioactive amount to the stable amount **Potassium-40 is useful in dating ancient rocks because of its long half life ** carbon. Carbon-14 is used to date fossils because all living things contain

Practice Questions _____ is used to determine the age of once-living artifacts? a) iodine-131 b) phosphorus-32 c) carbon-14 d) americium-241

Geologist use _____ to determine the absolute age of rocks. a) absolute age dating b) relative age dating c) radiation dating d) radioactive dating

Geologist use the time it takes for a radioactive isotope to decay to half its original mass called a______. a) radioactive decay b) isotope c) half-life d) carbon dating

• Which of the following is best used to date ancient rocks? a) iodine-131 b) potassium-40 c) carbon-14 d) uranium- 238

Geologic Time Scale- Record of the geologic events and evolution/extinction of life forms as shown in the fossil record. Used to show Earth’s history. **Remember life started out very simple and evolved to much more complex • They use evidence from – Rock layers (relative dating) – Index fossils – Radioactive dating • Era-three long units of time that divide time after Precambrian to present (Paleozoic- Age of Fish/Amphibians and Pangea formed, Mesozoicage of reptiles, dinosaurs and Pangea breaking apart Cenozoic—age of mammals evolved and continents moved to their present day positions) Precambrian = 88% of Earth’s history. • Period- Subdivisions of Eras – Names of many geologic periods come from places where geologists first described the rocks and fossils for that period

Geologic History and Biological Evolution Precambrian Time (not an era) 4. 6 billion years ago – 542 million years ago • Formation of earth 4. 6 billion years ago • 4 billion years ago—oceans form, they cover earth • First sedimentary rocks form 3. 8 billion years ago • Single celled organisms evolve to multi-celled near the end of the Precambrian • Formation of invertebrates (no backbone) Three Eras of Geologic Time (oldest to now) 1. ) Paleozoic (542 -251 mya) 2. ) Mesozoic (251 -66 mya) 3. ) Cenozoic (66 mya to present)

Paleozoic (542 -251 mya) “Age of Fishes/Amphibians” • 542 -444 mya Age of Invertebrates – First organisms with shells (beginning) – Trilobites dominate – First fishes (end) • 444 -359 mya “Age of Fishes” – First land plants (beginning) – Fishes dominate – First insect fossils (end) • 359 -251 mya “Age of Amphibians – Largest amphibians abundant, coal swamps (beginning) – Evolution of amniotic eggs: allowed animals to lay eggs without the egg drying out. – First reptiles – Extinction of trilobites, many other marine animals (end) • The Paleozoic Era ends with a mass extinction – 90% of ocean species and 70% of land species died out – Scientists not sure what caused extinction • Rise in global temperature • Multiple Volcanic eruptions released CO 2 and energy from the sun was blocked • Asteroid hit the Earth – ALL may have contributed

Mesozoic Era (251 -66 mya) AGE OF THE REPTILES • 251 -200 mya (Triassic Period) – First Dinosaurs appeared. – Small mammals appeared (size of a mouse) • 200 -146 mya (Jurassic Period) – Dinosaurs dominant land animals – First birds • 146 -66 mya (Cretaceous Period) – First flowering plants The Mesozoic Era ends with a mass extinction • Asteroid struck Earth—creating huge dust clouds • Wipes out more than half of all plant and animal groups

Cenozoic Era (66 mya to present) AGE OF THE MAMMALS • 66 -23 mya – Modern groups of mammals appear, grasses first spread widely • 23– 1. 8 mya – Large carnivorous and grazing mammals • 1. 8 mya to present – Humans develop