3/1 & 3/2 - 7th Grade Agenda (1st Period Writing Exam) Collect HW: Review & Reinforce p.95 & 98 Late Science Fair Presentations & Test for Absent Students Geological Time Scale Radioactive Decay Pass back graded HW & Test & Grade Printout Video: Walking w/ Monsters before Dinosaurs HW: Signed Grade Printout

Reflection Prompt: How can scientists know whether a rock is older than another rock?

What is relative age of a rock? The relative age of a rock is its age compared to the ages of other rocks

What is the absolute age of a rock? The absolute age of a rock is the number years since the rock was created.

Which layer is the oldest layer of rock? Bottom Layer is the Oldest Layer Law of superposition: In horizontal sedimentary rock layer the oldest layer is at the bottom. Each higher layer is younger than the layers below it.

What is Igneous Intrusion? Igneous Intrusion forms when magma cools and hardens beneath the surface Igneous intrusion is always younger than the rock layer around and beneath it.

Which is older? The fault or the rock layer? A fault is a break in earth’s crust. A fault is always younger than the rock it cuts through.

Why is there gaps in the Geologic Record? Unconformity is a gap in the geologic record.

What is an index fossil? Index fossils help geologists match rock layer To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed only briefly.

Which fossils are index fossils ? Trilobite Ammonite

These rocks are some of the oldest fossils in the world These rocks are some of the oldest fossils in the world. How old are they? Stromatolites: Remains of ocean reefs created by bacteria more than 3 billion years ago.

What is Radioactive Decay? Radioactive Decay: over time, unstable elements break down or decay by releasing particles and energy.

What is half-life? The half-life of a radioactive element is the time it takes for half of the radioactive atoms to decay.

If Geologic time went by in a single day, when did humans first appear? Humans first appear one second before midnight

Geological Time Scale Paleozoic: Paleo means ancient or early Mesozoic: Meso means middle Cenozoic: Ceno means recent