Which statements about geologic time are true? Check all that apply.

Scientists developed the geologic time scale as they studied rock layers and index fossils.
The fossil record helps scientists describe life only in the seas and other bodies of water.
Precambrian time is the most recent time in Earth’s history.
Precambrian time makes up 88 percent of Earth’s history.
The first birds appeared during the Jurassic period.
The basic units of the geologic time scale are periods, eras, and centuries.
Humans appeared during the Cenozoic era.

Geologic time scale description is given below

Explanation:

1.The geologic time scale is a system of chronological dating that relates geological stratigraphy to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

2.Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. With this information,scientists placed Earth's rocks in order by relative age. Later, radioactive dating helped determine the absolute age of the divisons in the geologic time scale.

3.Index fossils are of organisms that lived over a wide area. They lived for a fairly short period of time. An index fossil allows a scientist to determine the age of the rock it is in.

4.The Fossil Record -Fossils provide evidence that organisms from the past are not the same as those found today, and demonstrate a progression of evolution. ... The resulting fossil record tells the story of the past and shows the evolution of forms over millions of years.By studying the fossil record we can tell how long life has existed on Earth, and how different plants and animals are related to each other. Often we can work out how and where they lived, and use this information to find out about ancient environments. Fossils can tell us a lot about the past.

5.Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation about 4.5 billion years ago and ending with the emergence of complex, multicelled life-forms almost four billion years later.Around three billion years ago, the atmosphere of earth during the Precambrian time was virtually devoid of oxygen. The oxygen was produced as the byproduct of the photosynthetic activities of the cyanobacteria. The level of the gas raised and reached upto one percent about 2 billion years ago.The fossil collection in our museum begins about 750 million years ago, near the end of Precambrian time. The only multi-cellular life forms at the end of the Precambrian were in the oceans and included some groups that have survived until the present: jellyfishes and segmented worms (annelids).