2. WHAT IS GEOLOGIC TIME?
Geologic time is the chronology of the
Earth’s formation, changes, development, and existence. These events
are measured on a geological time scale. Scientists do not measure
geologic time on a clock or calendar. They use a linear timeline based
on the age of rocks and their corresponding fossils as well as the
change in life that occurred over millions of years.
3. WHAT IS A GEOLOGIC TIME SCALE? The geologic time scale is the
“calendar” for events in Earth’s history. The enumeration of those
geologic time units is based on stratigraphy, which is the correlation
and classification of rock strata.
4. ENUMERATE AND DEFINE EACH OF THE DIVISION OF GEOLOGIC
TIME SCALE
EONS- The eon is the broadest category of geological time. There are four
eons starting from the oldest to the youngest which are the Hadean,
Archean, Phanerozoic. Proterozoic and Hadean, Archean and Proterozoic are
also collectively known as the Pre-Cambrian Eon.
Hadean (4.6 - 4 billion years ago): Earth’s formation, heavy
bombardment, and formation of the earliest crust.
Archean (4 - 2.5 billion years ago): Development of Earth’s crust and
oceans; earliest evidence of life.
Proterozoic (2.5 billion - 541 million years ago): Oxygenation of the
atmosphere, emergence of multicellular life.
Phanerozoic (541 million years ago - present): Explosion of life forms,
including plants, animals, and eventually humans.
ERA- The smaller time interval that divides an EON. The Phanerozoic is
divided into three eras: Cenozoic, Mesozoic and Paleozoic. Very significant
events in the earth’s history are used to determine the boundaries of the era.
Paleozoic (541 - 252 million years ago): Era of ancient life, including
the development of fish, amphibians, and early plants.
Mesozoic (252 - 66 million years ago): Known as the "Age of Reptiles,"
it includes the rise and extinction of dinosaurs.
Cenozoic (66 million years ago - present): Known as the "Age of
Mammals," it includes the evolution of mammals and birds, and the
appearance of humans.
PERIODS- Just as eons are subdivided into eras, eras are subdivided into
units of time called periods. The most well-known of all geological periods is
the Jurassic period of the Mesozoic era (the movie Jurassic Park, of course,
has something to do with that). The Paleozoic era is divided into six periods.
From oldest to youngest, these are the Cambrian, Ordovician, Silurian,
Devonian, Carboniferous, and Permian.
Cambrian Period (Paleozoic Era): Explosion of marine life.
Jurassic Period (Mesozoic Era): Age of large dinosaurs and abundant
plant life.
Quaternary Period (Cenozoic Era): Development of humans and ice
age cycles.
EPOCHS- Shortest subdivision; marked by differences in life forms and can
vary from continent to continent
Tertiary Period
Paleocene Epoch: Mountain formation of the Alps, Himalayas,
Rockies, and Andes; flowering plants thrived, and mammals diversified.
Eocene Epoch: Atlantic and Indian oceans formed; tropical climate;
early horses, camels, and primitive apes appeared.
Oligocene Epoch: More land expansion and mountain building;
seasons became more defined; grasslands grew, and a possible human
ancestor emerged.
Miocene Epoch: Asia connected to Europe; varied climate; grasslands
expanded, and primitive humans began migrating from Africa.
Pliocene Epoch: Sierra Nevada and other ranges formed; climate
varied; pre-human ancestors increased in number.
B. Quaternary Period
Pleistocene Epoch: Repeated glaciation lowered sea levels, creating
land bridges; large mammals and early humans spread globally.
Holocene Epoch: Glaciers melted, raising sea levels; warmer climate;
humans developed agriculture, domesticated animals, and built
civilizations.
5. WHAT IS BIOSTRATIGRAPHY? Is the correlation of stratigraphic units
based on fossil content. Biostratigraphically useful species are known
as index fossils used as guides for recognition of chronostratigraphic
units
6. WHAT ARE INDEX FOSSILS? WHEN ARE THEY CONSIDERED AS
INDEX FOSSILS? Index fossils are widespread, have short temporal
durations resulting from rapid life spans, are abundant throughout their
geographic and geologic ranges, and are easily recognized (unique).
Be from an organism that was widely distributed across different regions.
Come from a species that existed only for a short period geologically, allowing
for precise dating.
Be easily recognizable.
7. DESCRIBE HOW INDEX FOSSILS (GUIDE FOSSILS) ARE USED TO
DETERMINE AND IDENTIFY SUBDIVISIONS OF GEOLOGIC TIME
SCALE
Index fossils help geologists and paleontologists correlate rock layers
across different regions. Because index fossils come from organisms that
existed during specific time periods, their presence in a rock layer helps
scientists pinpoint the layer’s age. By matching layers with similar index
fossils, scientists can create a timeline and identify subdivisions in the
geologic time scale, such as different periods or epochs.
8. ENUMERATE AT LEAST 5 INDEX FOSSILS.
Trilobites (e.g., Elrathia kingii), common in the Paleozoic Era.
Ammonites, particularly for the Mesozoic Era.
Brachiopods from various periods.
Foraminifera (e.g., Globigerina), useful in marine stratigraphy.
Graptolites, useful in dating Ordovician to Silurian rocks.
9. WHAT IS MATCHING? Matching is a process of correlating rock layers
of different location through the presence or absence of a certain index
fossil. Basically, this follows the faunal fossil succession principle.
10. WHAT IS THE WORK OF GEOLOGISTS AND
PALEONTOLOGISTS?
Geologists study the Earth’s structure, materials, and processes, including the formation of
rocks, minerals, and other natural features. They seek to understand Earth’s history and the
forces that shape its surface.
Paleontologists specialize in studying fossils to understand the evolution of life on Earth,
including ancient plants, animals, and ecosystems. They work to reconstruct prehistoric
environments and examine how life forms have changed over time.
