Fossils are rare in Precambrian rocks mostly
because Precambrian life-forms lacked bones, or other hard parts that commonly form fossils
. One of the few Precambrian fossils that have been discovered are stromatolites.
Why are Precambrian fossils rare?
Fossils are rare in Precambrian rocks, probably
because Precambrian life-forms lacked bones, shells, or other hard parts that commonly form fossils
. Also, Precambrian rocks are extremely old. Some date back nearly 3.9 billion years.
Why is there little fossil evidence from the Precambrian era?
The Precambrian fossil record
is poor
, and what fossils are present are of little use for biostratigraphic work. Many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.
Why are so few Precambrian rocks exposed on Earth's surface?
Due to the fact
that fossils from the Precambrian Period are limited
, very few fossils can be found in Precambrian-aged rocks and these mostly of single celled organisms that don't change much over long periods of times.
Why are fossils so uncommon in older rocks eg 1 billion years old )?
Because
only the earliest forms of life
(protozoa, algae, etc.) existed at that point in time three billion years ago, and those forms did not survive in the sediments that covered them at the bottom of the seas.
How old is the oldest fossil on Earth?
The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated
3.5 billion years old
. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old!
What era can the oldest fossils be found?
The oldest is
the Paleozoic Era
, which means “ancient life.” Fossils from the Paleozoic Era include animals and plants that are entirely extinct (e.g., trilobites) or are rare (e.g., brachiopods) in the modern world.
What did the Earth look like during the Precambrian era?
During this era the surface of the Earth was like popular visions about Hades:
oceans of liquid rock, boiling sulfur, and impact craters everywhere
! Volcanoes blast off all over the place, and the rain of rocks and asteroids from space never ends.
Why is the Precambrian era important?
The Precambrian is
the earliest of the geologic ages
, which are marked by different layers of sedimentary rock. Laid down over millions of years, these rock layers contain a permanent record of the Earth's past, including the fossilized remains of plants and animals buried when the sediments were formed.
What was life like during the Precambrian era?
The first protozoa appeared followed closely by worms. Soon after, arthropods, mollusks, and fungi showed up in the fossil record. The end of the Precambrian Time saw much more complex organisms like
jellyfish, sponges, and organisms with shells come into existence
.
What was the most common type of rock to be found during the Precambrian period?
Komatiite, a
magnesium-rich, high-temperature volcanic rock derived from very hot mantle (part of the Earth between the crust and the core), was extruded in abundance during the early Precambrian when the heat flow of the Earth was higher than it is today.
Where are the greatest areas of Precambrian rocks exposed at the surface?
Precambrian rocks often occur in shields, which are large areas of relatively low elevation that form parts of continental masses. One of the largest exposed areas of early Precambrian rocks is
the Canadian Shield
, where geologist Sir William Logan did his pioneer work.
What animals lived in Precambrian time?
The fossil record of multi-celled animals from the Precambrian includes three main groups that have persisted to the present day. These include the
sponges
, the cnidarians (including sea anemones, corals, and jellyfish) and the annelids, or segmented flatworms. Figure 1. Stromatolites and Precambrian prokaryotes.
Which kind of unconformity is probably the hardest to recognize among layered rocks?
Since
disconformities
are hard to recognize in a layered sedimentary rock sequence, they are often discovered when the fossils in the upper and lower rock units are studied.
How can you tell a rock from a fossil?
It is also a good idea to look for signs that the rock contains a fossil before trying to break it, part of a fossil may be visible on the surface of the rock. You can identify the limestone by it's
lighter grey colour and hardness
, it should be quite hard to break without a hammer.
Why are fossils so uncommon in older rocks Group of answer choices?
Why are fossils so uncommon in older rocks? …
A rock stratum is tilted noticeably from horizontal
.
