ISP 203A Geologic Time

What do scientists study to estimate the age of rocks and Earth history?

They use methods such as relative dating and absolute dating, plus context clues from rock layers and fossils.

What is the difference between relative dating and absolute dating?

Relative dating places events in sequence without knowing exact ages; absolute dating assigns a numerical age.

Ancient Greeks described marine fossils as far back as…

570 BCE

Ancient Persian, Chinese, Indian, and European texts discuss…

Finding of fossils

Fossils may have inspired….

Myths & legends of fantastical creatures

Word “Paleontology” first appeared in…

1822

Early stratigraphy and comparative anatomy influenced…

Darwin’s theory of evolution by natural selection.

Who was Shen Kuo, and what did he contribute to geologic time studies?

Song Dynasty statesman and scholar (11th century).

First to describe magnetic compass use.

Studied marine fossil deposits → hypothesized erosion, land movement, and paleontology.

Concluded climate was once very different in his region based on bamboo fossils

Stratigraphy

interpreting rock layers

Biostratigraphy

using fossils

Radiometric Dating

Measuring a radioactive element & its daughter products

When did Earth form, and what were the main stages?

~4.6 Ga; stages included accretion (layering), collision with a protoplanet (moon formation, ~4.5 Ga), and asteroid bombardment (possibly delivered water).

Ga

Giga Annum = billion years

Ma

Mega Annum = million years

Ka

Kilo Annum = thousand years

How old is Earth, and when did multicellular life appear?

Earth is ~4.56 Ga; multicellular life appears around 600 Ma.

How is geologic time divided and named?

Using GSSPs (Global Boundary Stratotype Section and Point), fossil evidence, multiple defining features, and absolute dating.

What are the four Earth spheres?

Atmosphere (air, weather, climate), Biosphere (life), Hydrosphere (water), Geosphere (rocks, magma).

Give one internal process and one interaction between Earth spheres.

Geosphere process = volcanic eruption. (internal) Atmosphere interaction = volcano releases gases into air. (external)

How do stars form?

Stars form inside molecular clouds (dense regions of gas and dust).

Gravity causes the cloud to collapse into dense clusters.

These condense further into a protostar (an early-stage star).

As collapse continues, temperature and pressure rise in the core.

When core pressure is high enough, nuclear fusion begins, marking the birth of a true star.

What happens during stellar nucleogenesis?

atoms of hydrogen fuse together to make helium, releasing energy in the process.

Eventually, heavier atoms like carbon & oxygen will form through this process if the star is big enough

Largest stars eventually form iron (heaviest element a star can form through interior infusion)

How do stars die?

Smaller stars lose their outer layers in life & form planetary nebulae

very large stars that produce iron quickly collapse & explode in a supernova

All other elements are created in this blast