GEO 1306 Exam 2

Rates of change in the present and the past

Earth changes catastrophically (fast) or gradually (slow) change

Present: we can see both happening → earthquakes (fast) plate movement (slow)

Law of Uniformitarianism and how do we apply it?

natural processes shaping the Earth today (erosion, sedimentation, and volcanic activity) the same processes that operated in the past. We look at modern examples and use them to understand the past.

Relative dating

determining the relative order of past events

Absolute dating

measure the physical properties of an object itself and use these measurements to calculate its age

Radiometric dating and how is it done?

measures the ratio of radioactive parent isotopes to stable daughter products

Half-lives

the amount of time it takes for ½ of remaining parent particles to decay

Decay rate

asymptotic curve of decay rate (never reaches 0)

Combining relative dating and absolute dating

relative dating determines sequences of events, and absolute dating provides numerical ages, allowing scientists to assign exact ages to fossils and rock layers

The Geologic Timescale

a system used to organize Earth’s history into units of time based on fossil evidence (relative dating) and radiometric dating (absolute dating)

The Eons

• Hadean (4.6-4.0 billion years ago)

• Archean (4.0-2.5 billion years ago)

• Proterozoic (2.5-0.55 billion years ago)

• Phanerozoic (0.55 billion years ago-present)

Formation of the Solar System

formed froma. stellar nebula (cloud of gas and dust) that collapsed under gravity. most material formed the Sun, while the remaining material accreted into planets and moons

Age of the Solar System

~4.53-4.58 billion years old

Evidence for Age of Solar System

determined using radiometric dating of meteorites, which are leftover material from solar system formation and have not been altered

Formation of Earth

formed through gravitational accretion, where dust and particles collided and stuck together, gradually forming a larger rocky planet

Age of the Earth

~4.5 billion years old

Evidence for the Earth

• Meteorites (~4.5 billion years old)

• Moon rocks (~4.4 billion years old)

• Oldest Earth rocks (3.8-4.28 billion years old)

Formation of Earth’s Layers

formed through differentiation while the planet was molten

• dense materials (like metals) sank to the core

• lighter materials rose to the crust

Start of Earth’s Magnetic Field

began when the liquid outer core started moving and spinning, generating a magnetic field that protects Earth from solar radiation

Formation of the Moon

formed from the giant impact hypothesis, where a Mars-sized object (Theia) collided with Earth, and the ejected material combined to form the Moon

Evidence for Theia Impact Hypothesis

• Moon is mostly made of felsic (crust-like) material

• Moon lacks dense/heavy elements

• Earth and Moon have aligned orbital planes

• Explained by conservation of angular momentum

Heavy Bombardment Period

a time when many leftover planetesimals frequently impacted Earth and the Moon, creating many craters

Significance of the Isua Greenstone

provides evidence of some of the oldest rocks on Earth, early liquid water (pillow basalts, sedimentary features), early geological processes like erosion and volcanism

The modern ocean

covers 70% of Earth’s surface and is essential for life, climate, and recording geological events. Ocean water is salty mostly sodium chloride, with calcium ions important for forming limestone

Archean evidence of liquid water

rocks like pillow basalts and sedimentary deposits show that liquid water existed by the Archean Eon. Sea surface temperature 17°C and global surface temperatures were about 15°C

Possible sources of water on Earth

Earth’s water came from both terrestrial and extraterrestrial sources

Extraterrestrial source

include icy comets during the heavy bombardment phase

Terrestrial source

water bound in mantle minerals was released by volcanoes

Goldilocks zone hypothesis

Earth is at the right distance from the Sun: not too cold, not too hot. This liquid water to exist and made life possible

The modern atmosphere

78% nitrogen, 21% oxygen, 1% argon, and 0.04% carbon dioxide. oxygen is essential for life, and CO₂ supports photosynthesis and climate regulation

Source of atmosphere

nitrogen from volcanic gases and accumulated because it is inert. Oxygen was produced by photosynthesis, first by ancient bacteria like those in stromatolites

Archean and Proterozoic oxygen

banded iron formations (BFIs) show that oxygen began entering the oceans around 3.8 billion years ago, causing iron to precipitate. Red beds, appearing around 2.2 billion years ago, show oxygen accumulation on land. Oxygen levels rose gradually from the Archean and peaked in the Proterozoic

Energy in

Earth gets energy from the Sun

Greenhouse Effect

traps some heat leaving Earth as infrared radiation, keeping the planet warm.

Solar luminosity

the Sun’s total energy output and solar insolation is how much reaches Earth.

Solar insolation

how much energy reaches the Earth

Energy out

Energy leaves as black body radiation, and the balance of incoming and outgoing energy controls climate

What is an Icehouse World?

where there is stable ice sheets at the poles (lasts year round)

What is a Greenhouse World?

when there is no stable ice at the poles

Oxygen isotope fractionation - what is it used for?

the ratio of ¹⁸O to 1⁶O in ocean water records past temperatures. More ¹⁸O indicates colder oceans (ice traps ¹⁶O), while less ¹⁸O indicates warmer oceans

Snowball Earth

late Proterozoic, when glaciers and sea ice reached the equator. Evidence includes glacial deposits, drop stones, and Banded Iron Formations (BFIs)

Banded Iron Formations

layers of iron oxides that indicate ancient oxygen in oceans, especially common during Snowball Earth periods