WEEK 5 - Our perception of Time and the Antiquity of Earth Flashcards

Question

How Does Angular Unconformity FORM?

Answer 1

Older layers are deposited → tilted → eroded → buried by younger layers Represents a gap in the geologic record due to missing time (erosion)

Answer 2

By using atomic clocks in minerals Each element has a fixed number of protons, but neutron numbers can vary Atoms of the same element with different atomic weights are called isotopes

Answer 3

Some isotopes (parent isotopes) lose particles from their nucleus This forms a new element (daughter isotope) Energy is released in the process 🔄 This process is called radioactive decay

Answer 4

PROTONS: Positively charged (+) particles Found in the nucleus of an atom NEUTRONS: Neutral (no charge) particles Found in the nucleus of an atom ELECTRONS: Negatively charged (-) particles Move around the nucleus in energy levels (shells) NUCLEUS: The dense central core of an atom Contains protons (+) and neutrons (0) Holds almost all the atom’s mass

Answer 5

As a parent isotope decays, daughter isotopes accumulate The ratio of daughter to parent isotopes increases over time More daughter isotopes = Older rock sample

Answer 6

The time it takes for half of the parent atoms to decay into daughter atoms Each half-life represents the halving of the previous amount of parent isotopes

Answer 7

📊 What do different ratios tell us? 1:1 (½ parent left) = One half-life passed 1:3 (¼ parent left) = Two half-lives passed 1:7 (⅛ parent left) = Three half-lives passed 1:15 (1/16 parent left) = Four half-lives passed

Answer 8

Used to date igneous rocks Measures the ratio of Potassium-40 (parent isotope) to Argon-40 (daughter isotope) Decay starts when minerals crystallize from magma

Answer 9

⚛ What does the parent-daughter ratio tell us? More Argon-40 → Older sample Half-life of Potassium-40 = 1.25 billion years If 1/4 parent isotope remains (1:3 ratio) → 2 half-lives passed → Sample = 2.5 billion years old

Answer 10

✅ Igneous rocks (e.g., feldspar, mica) ✅ Intrusive bodies (e.g., dykes, sills) ❌ Sedimentary rocks CANNOT be directly dated

Answer 11

📏 How can igneous rocks help date sedimentary layers? Igneous intrusions or ash layers in sedimentary strata provide age brackets Example: - Dakota Sandstone → Estimated between 160 & 66 million years old

Answer 12

A "master timetable" for Earth’s history Based on relative dating (fossils) & absolute dating (radiometric techniques) Divides Earth’s history into eons, eras, periods, and epochs

Answer 13

1️⃣ Provides a framework for studying Earth's history 2️⃣ Makes scientific communication easier 3️⃣ Helps define large & small time units

Answer 14

1️⃣ Eon = Largest unit 2️⃣ Era = Subdivision of eon 3️⃣ Period = Subdivision of era 4️⃣ Epoch = Subdivision of period

Answer 15

1️⃣ Hadean (oldest) 🌋 ~4.6 billion years ago 2️⃣ Archean 🦠 ~4.0 billion years ago 3️⃣ Proterozoic 🧬 ~2.5 billion years ago 4️⃣ Phanerozoic ("visible life") 🦖 ~541 million years ago (most recent)

Answer 16

1️⃣ Paleozoic = “Ancient Life” 🐠 2️⃣ Mesozoic = “Middle Life” 🦖 3️⃣ Cenozoic = “Recent Life” 🐘

Answer 17

1️⃣ Type localities – Named after locations (e.g., Jurassic from Jura Mountains) 2️⃣ Rock characteristics – Based on features like coal deposits (e.g., Carboniferous) 3️⃣ Whims & history – Inspired by cultural references (e.g., Silurian from a Celtic tribe)

Answer 18

A “master timetable” of Earth's history Based on relative time (sequence of events) & absolute time (radiometric dating) Organized hierarchically into large & small time units

Answer 19

Cambrian – Explosion of life, first hard-shelled organisms Ordovician & Silurian – First fish, early land plants Carboniferous – Coal-forming forests, giant insects 🦗 Jurassic – Dinosaurs dominate 🦖 Cretaceous – Flowering plants appear 🌸, dinosaurs go extinct Quaternary – Humans appear 👣

Answer 20

📏 What are the major time boundaries in millions of years? Hadean → Archean: ~4.0 billion years ago Archean → Proterozoic: ~2.5 billion years ago Proterozoic → Phanerozoic: 541 million years ago