140 Million Years on Earth

Earth Coastlines Through Time

The theme for day five of the #30DayMapChallenge is Earth. What better way to explore this theme than to map how the Earth's land masses have shifted, collided, and drifted apart over geological time?

My Earth Coastlines Through Time map lets you see how Earth’s coastlines and continents have shifted voer 140 million years, from the Early Cretaceous period to the present day.

What the Map Shows

The map provides a visual timeline of Earth's coastlines, showing major geological events such as:

• The breakup of Gondwana
• The opening of the Atlantic Ocean
• India’s collision with Asia and the rise of the Himalayas
• The isolation of Antarctica
• The arrival at Earth’s modern continental configuration

A slider control allows you to move through time, updating the coastlines and displaying relevant geological information in a sidebar. You can also adjust the underlying basemap’s opacity to compare ancient and present-day coastlines.

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How the Map Works

The map is built using MapLibre GL JS, an open-source alternative to Mapbox GL. Key features include:

• Timeline slider: Moves through eight time slices from 140 Ma to today.
• Coastline layers: Each geological time slice is represented as a GeoJSON layer with the coastlines drawn on top of the basemap.
• Sidebar: Shows contextual information about the geological period currently displayed.
• Opacity control: Lets you fade in or out the modern OpenFreeMap basemap to better see ancient coastlines.
• Custom attribution: Credits OpenStreetMap, GPlates.

The interface is responsive, so the sidebar moves below the map on mobile devices, while the timeline and opacity sliders remain centered for easy interaction.

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Where the Data Comes From

The coastline data for each time period comes from GPlates, an open-source tool for plate tectonics visualization. GPlates provides global reconstructions of Earth’s coastlines through geological time. 

The basemap used is OpenFreeMap’s Positron style, giving a clean, minimal background that emphasizes the coastlines.