Question

Dinosaurs first appear in the geological record in rocks at 225 Ma and then disappear at 65 Ma. For what proportion (\%) of geological time did dinosaurs exist?

Short answer

Dinosaurs existed for approximately \(160\) million years, which is about \(\frac{160}{4600}\) or \(3.48 \%\) of geological time.

Step-by-step solution

Find the duration of dinosaurs' existence

To determine the length of time that dinosaurs existed, subtract the year of their disappearance (65 Ma) from the year of their first appearance (225 Ma): Duration of dinosaurs' existence = \(225 - 65\) Duration of dinosaurs' existence = \(160\) million years.

Calculate the proportion of geological time

To find the proportion of geological time that dinosaurs existed, divide the duration of their existence (160 million years) by the entire history of Earth (4600 million years): Proportion = \(\frac{160}{4600}\)

Convert the proportion to a percentage

Multiply the proportion we found in Step 2 by 100 to convert it into a percentage: Percentage = Proportion × 100 Percentage = \(\frac{160}{4600}\) × 100 Percentage = 0.0348 × 100 Percentage ≈ 3.48 % So, dinosaurs existed for approximately 3.48% of geological time.

Key concepts

Dinosaurs

Dinosaurs once roamed the Earth and dominated the land for millions of years. Their existence started around 225 million years ago and lasted until about 65 million years ago. This period is known as the Mesozoic Era, a time when dinosaurs were the most prominent species among other reptiles.
Dinosaurs are fascinating not only because of their size and diversity, but also because they left behind a wide range of fossils. These fossils help scientists understand life on Earth millions of years ago. Fossils can include bones, teeth, eggs, and even footprints.
These prehistoric creatures are grouped into different types based on their hip structures, which are either bird-hipped or lizard-hipped. There's a vast variety of dinosaurs that adapted to land, sea, and air:

• Herbivores like the Triceratops, which fed on plants.
• Carnivorous predators like the Tyrannosaurus rex, known for their fierce hunting abilities.
• Flying dinosaurs like Pterosaurs, which lived in the skies above their larger cousins.

Understanding dinosaurs' lifestyles gives us insight into past ecosystems and how environments changed over time.

Geological Record

The geological record is like a time capsule of Earth's history, preserved within layers of rock that have accumulated over billions of years. These layers, called strata, are formed by various geological processes such as sedimentation, volcanic eruptions, and tectonic activity.
Each layer can tell a story about a specific time period in Earth's history. Fossils found within these layers give evidence of past life forms, including the era when dinosaurs ruled the Earth. Geologists study these layers to determine the age of rocks and fossils and to reconstruct past environments.
The knowledge gained from the geological record helps us understand long-term changes in Earth's climate and the evolution of life. It's crucial for identifying and correlating layers worldwide, which helps depict a timeline of Earth's history.
Key components of the geological record that are often studied include:

• Fossil content, which helps to identify the age and environment of the rocks.
• Stratigraphy, the study of rock layers and layering.
• Radiometric dating, which measures the decay of radioactive elements to determine age.

These tools and concepts allow scientists to trace the transition of life forms throughout Earth's past, providing a comprehensive view of evolutionary history.

Earth's History

Earth's history spans over 4.6 billion years and is marked by dramatic changes and landmark events. These changes have shaped the planet's surface and the life that it supports. Geologists divide Earth's long history into different eons, eras, periods, and epochs to better understand the events that have occurred.
Four main eons help outline Earth's vast history, each characterized by distinct geological and biological developments:

• Hadean Eon: Beginning with the formation of the Earth, this eon saw a molten surface gradually solidifying into a crust.
• Archean Eon: The Earth's crust stabilized, and life began with the advent of simple single-celled organisms.
• Proterozoic Eon: Marked by the rise of more complex life forms and the first oxygen-rich atmosphere.
• Phanerozoic Eon: The most recent eon, which saw the rapid diversification of life, including the age of dinosaurs and the appearance of mammals and humans.

Each of these periods involved massive shifts, such as ice ages, continental drift, and mass extinctions, including the one that led to the disappearance of the dinosaurs. By studying these events, scientists can predict future trends in climate and biodiversity, offering insights into how our planet continues to change today.