Exam 24: The History of Life on Earth

Refer to the graph showing variations in oxygen levels during Earth's history. Based on the graph, what is the most logical conclusion about the abundance of plant life in the time interval about 250 million years ago?

A pure radioactive substance has a mass of 30 micrograms but had a mass of 240 micrograms 48 years ago.Assuming that the only changes in mass are due to radioactive decay, the half-life of the substance is _______ years.

At the global level, changing environmental conditions are currently characterized by a(n) increase in temperature caused by increased levels of _______ in the atmosphere.

Refer to the figure depicting a layer of Iridium at the Cretaceous-Tertiary (K/T) boundary between strata from two different periods in Earth's history. Explain the significance of the globally distributed iridium layer found in strata with an age of approximately 65.5 million years.Explain which kinds of species went extinct at this time, and why (be as specific as possible).

In undisturbed sedimentary rock, strata from the _______ are immediately above rocks from the Ordovician.

Based on the results of experiments raising flies at higher levels of oxygen, which of the following statements is most probable?

At very small population densities, local extinctions can be caused by accidents such as not being able to find a mate.Examples of such phenomena are referred to collectively as the _______ effect.

If 50 mg of a radioactive substance becomes 12.5 mg in 2,600 years, the half-life of the substance is _______ years.

Among terrestrial species, those adapted to _______ conditions (such as higher elevations) are expected to be particularly vulnerable to climate change.

You have discovered a nonavian dinosaur fossil in a sedimentary stratum with a nearby igneous intrusion.Based on this description, which type of analysis would not be appropriate for this sample?

Which statement is true?

The Ottawa-Bonnechere Graben is a region in Canada characterized by two continental plates moving away from one another.The resulting geological feature is called a _______.

One billion years ago, Earth was in the _______ eon.

Refer to the figure. The figure shows the _______ era, during which atmospheric O₂ levels were almost equal to that of the present, and hard-bodied invertebrates were abundant and diverse in the sea.

The Cenozoic era began about _______ years ago.

Refer to the figure, which illustrates changes in sea level over time.Asterisks indicate mass extinctions of marine organisms. Which statement is supported by the figure?

Refer to the figure, which shows an imaginary name scheme for an undisturbed site with distinct fossil assemblages in the top five layers of strata. Imagine that the Ware layer contains abundant and diverse shellfish and other marine fauna, while Sunderland contains the flora and fauna associated with lowland swamps. Which hypothesis is the most logical explanation to account for this?

Over geologic time, the concentration of O₂ in Earth's atmosphere has increased.However, at the end of the _______ period, the O₂ concentration decreased significantly and was associated with _______.

Which of the following is in the corrrect order, from largest to smallest?

Vertebrates with well-protected eggs that can be laid in dry places originated during the Carboniferous period.These animals are known as