diff --git a/milestones-data.js b/milestones-data.js
index 613f2e0..7769a7e 100644
--- a/milestones-data.js
+++ b/milestones-data.js
@@ -336,6 +336,20 @@ const MILESTONES = [
     darkColor: "#33691e",
     reference: "https://www.ipcc.ch/report/ar6/syr/",
   },
+  {
+    id: "human_extinction",
+    name: "Human Extinction Horizon",
+    icon: "💀",
+    tokens: 77000000000000000,
+    shortDesc: "77 Quadrillion Tokens",
+    description: "Climate tipping points cascade simultaneously — the window for human survival closes",
+    consequence: "By 77 quadrillion tokens, multiple simultaneous tipping points have been crossed: the West Antarctic Ice Sheet enters irreversible collapse, the Amazon transitions to savanna, and Arctic summer sea ice disappears permanently. These feedbacks amplify each other. Global temperature is locked in at +3°C — a level incompatible with large-scale organised human society. Food systems fail. Mass displacement begins. Modern civilisation loses its ability to function.",
+    followingEvent: "🌡️ The last generation to know a stable climate is alive today. Their children inherit a planet in permanent crisis.",
+    color: "#1a0000",
+    darkColor: "#0d0000",
+    reference: "https://www.science.org/doi/10.1126/science.abn7950",
+    extinctionMarker: true,
+  },
   {
     id: "grid_breaking_point",
     name: "Grid Infrastructure Breaking Point",
diff --git a/milestones.yaml b/milestones.yaml
index cd85ecc..b363769 100644
--- a/milestones.yaml
+++ b/milestones.yaml
@@ -434,6 +434,26 @@ milestones:
     darkColor: '#33691e'
     reference: 'https://www.ipcc.ch/report/ar6/syr/'
 
+  - id: human_extinction
+    name: Human Extinction Horizon
+    icon: "\U0001F480"
+    tokens: 77000000000000000
+    shortDesc: 77 Quadrillion Tokens
+    extinctionMarker: true
+    description: "Climate tipping points cascade simultaneously — the window for human survival closes"
+    consequence: >-
+      By 77 quadrillion tokens, multiple simultaneous tipping points have
+      been crossed: the West Antarctic Ice Sheet enters irreversible collapse,
+      the Amazon transitions to savanna, and Arctic summer sea ice disappears
+      permanently. These feedbacks amplify each other. Global temperature is
+      locked in at +3°C — a level incompatible with large-scale organised
+      human society. Food systems fail. Mass displacement begins. Modern
+      civilisation loses its ability to function.
+    followingEvent: "\U0001F321️ The last generation to know a stable climate is alive today. Their children inherit a planet in permanent crisis."
+    color: '#1a0000'
+    darkColor: '#0d0000'
+    reference: 'https://www.science.org/doi/10.1126/science.abn7950'
+
   - id: grid_breaking_point
     name: Grid Infrastructure Breaking Point
     icon: "\U0001F50B"
diff --git a/script.js b/script.js
index 95edd52..4b5ec2d 100644
--- a/script.js
+++ b/script.js
@@ -381,7 +381,9 @@
   }
 
   // ---- Life Blocks ----------------------------------------
-  const LB_LAST_MILESTONE = MILESTONES[MILESTONES.length - 1];
+  // Use the milestone tagged extinctionMarker:true as the life-blocks countdown target.
+  // Falls back to the last milestone only if no marker is found (defensive guard).
+  const LB_LAST_MILESTONE = MILESTONES.find(m => m.extinctionMarker) || MILESTONES[MILESTONES.length - 1];
 
   // Drill-down state
   const lb = {
diff --git a/scripts/build-milestones.js b/scripts/build-milestones.js
index 561ce12..eae9e08 100644
--- a/scripts/build-milestones.js
+++ b/scripts/build-milestones.js
@@ -89,6 +89,9 @@ function renderMilestone(m) {
   if (m.reference) {
     lines.push(`    reference: ${jsString(m.reference)},`);
   }
+  if (m.extinctionMarker) {
+    lines.push(`    extinctionMarker: true,`);
+  }
   lines.push('  }');
   return lines.join('\n');
 }