geologic time scale

geologic time condensed to one year

Its always fun to think about geologic time in a framework that we can more readily understand. Here are when some major events in Earth history would have occurred if all of earth history was condensed down to one calendar year. January 1 12 am: Earth forms from the planetary nebula - 4600 million years ago February 25, 12:30 pm: The origin of life; the first cells - 3900 million years ago March 4, 3:39 pm: Oldest dated rocks - 3800 million years ago March 20, 1:33 pm: First stromatolite fossils - 3600 million years ago July 17, 9:54 pm: first fossil evidence of cells with nuclei - 2100 million years ago November 18, 5:11 pm: Cambrian Explosion - 544 million years ago December 1, 8:49 am: first insects - 385 million years ago December 2, 3:54 am: first land animals, amphibians - 375 million years ago December 5, 5:50 pm: first reptiles - 330 million years ago December 12, 12:09 pm: Permo-Triassic Extinction - 245 million years ago December 13, 8:37 pm: first dinosaurs - 228 million years ago December 14, 9:59 am: first mammals 220 million years ago December 22, 8:24 pm: first flowering plants - 115 million years ago December 26, 7:52 pm: Cretaceous-Tertiary Extinction - 66 million years ago December 26, 9:47 pm: first ancestors of dogs - 64 million years ago December 27, 5:25 am: widespread grasses - 60 million years ago December 27, 11:09 am: first ancestors of pigs and deer - 57 million years ago December 28, 9:31 pm: first monkeys - 39 million years ago December 31, 5:18 pm: oldest hominid - 4 million years ago December 31, 11:02 pm: oldest direct human ancestor - 1 million years ago December 31, 11:48 pm: first modern human - 200,000 years ago December 31, 11:59 pm: Revolutionary War - 235 years ago

the geologic time scale

To be able to discuss Earth history, scientists needed some way to refer to the time periods in which events happened and organisms lived. With the information they collected from fossil evidence and using Stenos principles, they created a listing of rock layers from oldest to youngest. Then they divided Earths history into blocks of time with each block separated by important events, such as the disappearance of a species of fossil from the rock record. Since many of the scientists who first assigned names to times in Earths history were from Europe, they named the blocks of time from towns or other local places where the rock layers that represented that time were found. From these blocks of time the scientists created the geologic time scale (Figure 1.1). In the geologic time scale the youngest ages are on the top and the oldest on the bottom. Why do you think that the more recent time periods are divided more finely? Do you think the divisions in the scale below are proportional to the amount of time each time period represented in Earth history? In what eon, era, period and epoch do we now live? We live in the Holocene (sometimes called Recent) epoch, Quaternary period, Cenozoic era, and Phanerozoic eon.


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the geologic time scale was originally based

a) entirely on absolute ages.

b) on a mix of relative and absolute ages.

-->  c) entirely on relative ages.

d) on random events.

time units on the geologic time scale are

a) divided into 10 million year blocks.

-->  b) separated by important events in geological or biological history.

c) divided using absolute age dates.

d) separated by distinctive rock units.

we live in the holocene epoch, as well as the

a) quaternary period

b) cenozoic era

c) phanerozoic eon

-->  d) all of the above

if earth history is condensed into one calendar year, dinosaurs appear

a) in late february.

b) in mid-september.

-->  c) in mid-december.

d) on the night of december 31st.

if earth history is condensed into one calendar year, the first modern humans appear

a) in late september.

b) in mid-november

c) in mid-december.

-->  d) on the night of december 31st.

naming time periods makes it easier to talk about them.

-->  a) true

b) false

about 1/8 of earth history passed before the explosion of life forms in the cambrian.

a) true

-->  b) false

many of the blocks of time on the geologic time scale were named for

-->  a) nearby towns where the rock layer from that time were found.

b) locations in north america.

c) the geologists who worked in those rock sections.

d) all of these.

eon, era, period, epoch is the order from the largest amount of time to the smallest amount of time.

-->  a) true

b) false

compared with older time periods, more recent time periods on the geologic time scale

-->  a) are divided into more segments.

b) are about as well understood.

c) are more difficult to learn about.

d) all of these.

diagram questions

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